Process for producing composite prepreg base, layered base, and fiber-reinforced plastic

ABSTRACT

A composite prepreg base which includes a raw prepreg base comprising a fiber sheet comprising discontinuous reinforcing fibers arranged in one direction and having a fiber length of 1-300 mm and a matrix resin infiltrated into the fiber sheet; and an additional resin layer formed on at least one surface of the raw prepreg base. The composite prepreg base is produced by a process including (i) the step of preparing the raw prepreg base and (ii) the step of forming an additional resin layer on at least one surface of the raw prepreg base prepared. Also provided are: a layered base including two or more sheets of the composite prepreg base which have been superposed so that the additional resin layer is present on at least one surface; and a fiber-rein-forced plastic formed by heating and pressing the layered base.

RELATED APPLICATIONS

This is a §371 of International Application No. PCT/JP2007/068401, withan international filing date of Sep. 21, 2007 (WO 2008/038591 A1,published Apr. 3, 2008), which is based on Japanese Patent ApplicationNo. 2006-264785, filed Sep. 28, 2006.

TECHNICAL FIELD

This disclosure relates to a process for producing a composite prepregbase, and also relates to a layered base comprising a plurality of thecomposite prepreg bases laminated each other, and a fiber reinforcedplastic formed with the layered base.

BACKGROUND

A fiber reinforced plastic (hereinafter also referred to as FRP)comprising reinforcing fibers and a matrix resin has gained greaterattention in industrial fields because of having a high specificstrength, a high specific modulus, good mechanical characteristics, andother highly functional characteristics such as weather resistance andchemical resistance, and demands for them is increasing every year.

The most widely used molding method for producing an FRP haying highlyfunctional characteristics is an autoclave molding process in which alayered body produced by laminating a plurality of prepreg bases each ofwhich is prepared by impregnating a sheet comprising continuousreinforcing fibers with a semi-cured matrix resin, is heated and pressedin an autoclave and the matrix resin is cured to mold an FRP.

The FRP produced by the autoclave molding process is composed of thereinforcing fibers being in continuous and therefore has good mechanicalproperties. Furthermore, where the continuous fibers are arrangedregularly, such as in one direction, it will be easy to design an FRPhaving desired mechanical properties by arranging the prepreg baseplates in an appropriate configuration or alignment, and the resultingFRP products will be small in variation of mechanical properties.

However, on the other hand, it is difficult to produce an FRP having acomplicated shape such as three-dimensional, since the reinforcingfibers in the prepreg base are in continuous, and therefore,conventional FRP products have been limited to planar or nearly planarshapes.

A press molding process that uses a SMC (sheet molding compound) is oneof the molding methods that serve to mold an FRP having a complicatedshape such as a three-dimensional shape. In this molding process,chopped strands, normally cut into pieces of about 25 mm, areimpregnated with a matrix resin to provide a SMC sheet comprisingpartially cured resin, which is then heated and pressed by using a pressmachine to produce an FRP. In most cases, the SMC is cut into sheetseach of which is smaller than a molding FRP before the pressing, thesheets are placed on a mold, and the sheets are extended by pressing, ormade to flow, into a desired shape. Thus, the flowing allows thematerial to be molded into a complicated shape such as athree-dimensional shape.

However, the chopped strands inevitably suffer uneven distribution andorientation during the SMC sheet forming step, and therefore, theresulting FRP product will have poor mechanical properties that varylargely over the product, causing some problems. Moreover, in the caseof thin components, in particular, the molded products tend to sufferwarp and shallow depressions etc. in the surface, often leading todecreased suitability as components of structural materials.

To eliminate such disadvantages in the above-mentioned FRP materials andtheir production processes, an improved FRP production method has beenproposed in which deep cuts are put in a prepreg base that is composedof continuous fibers and a thermoplastic resin, in such a way that cutsare put in the continuous fibers in the direction across the continuousfibers, with the aim of increasing the flowability of the fibers duringa molding process and decreasing the variation in the mechanicalproperties in the resulting moldings (JP 63-247012 A).

In the prepreg base described in JP 63-247012 A, however, cuts aresimply put in the prepreg base though thermoplastic resin having a highmelt viscosity is used as matrix, and therefore, if an attempt is madeto produce a molded product having undulating portions, it will beimpossible riot only to achieve such an undulating shape precisely butalso maintain a high flowability of the prepreg base itself and that ofthe fibers in the prepreg base that are no longer continuous after beingcut to limited lengths.

It could therefore be helpful to provide a method for producing aprepreg base having a good flowability of the prepreg base itself and/orfibers having a certain length and being not continuous which isprepared with cuts of fibers in the prepreg base, having a goodfollowability to a shape of an intended mold, and having a wide range ofselecting molding conditions, at the time of molding a mold.

It could also be helpful to provide a layered base that can be moldedinto an FRP product having excellent mechanical properties, qualitystability, and appearance quality, and also provide FRP products thatcan be produced from the prepreg base or the layered base.

SUMMARY

We thus provide methods for producing a composite prepreg basecomprising a raw prepreg base composed of a fiber sheet of discontinuousreinforcing fibers having a fiber length of 1 to 300 mm and arranged inone direction and a matrix resin impregnated into the fiber sheet, andan additional resin layer formed on at least one of the surfaces of theraw prepreg base, which comprises the steps of:

-   -   (1-a) preparing a prepreg base comprising a fiber sheet of        continuous reinforcing fibers arranged in one direction and a        matrix resin impregnated at least partly into the fiber sheet,    -   (1-b) forming an additional resin layer on at least one of the        surfaces of the prepreg base prepared in the step (1-a), and    -   (1-c) forming cuts into the prepreg base having the additional        resin layer formed in the step (1-b) to form discontinuous        reinforcing fibers having a fiber length of 1 to 300 mm from the        continuous reinforcing fibers.

We also provide methods for producing a composite prepreg basecomprising a raw prepreg base composed of a fiber sheet of discontinuousreinforcing fibers having a fiber length of 1 to 300 mm and arranged inone direction and a matrix resin impregnated into the fiber sheet, andan additional resin layer formed on at least one of the surfaces of theraw prepreg base, which comprises the steps of:

-   -   (2-a) preparing a prepreg base comprising a fiber sheet of        continuous reinforcing fibers arranged in one direction and a        matrix resin impregnated at least partly into the fiber sheet,    -   (2-b) forming cuts into the prepreg base prepared in the step        (2-a) to form discontinuous reinforcing fibers having a fiber        length of 1 to 300 mm from the continuous reinforcing fibers,        and    -   (2-c) forming an additional resin layer on at least one of the        surfaces of the prepreg base having the discontinuous fibers        having the fiber length of 1 to 300 mm prepared in the step        (2-b).

We further provide methods for producing a composite prepreg basecomprising a raw prepreg base composed of a fiber sheet of discontinuousreinforcing fibers having a fiber length of 1 to 300 mm and arranged inone direction and a matrix resin impregnated into the fiber sheet, andan additional resin layer formed on at least one of the surfaces of theraw prepreg base, which comprises the steps of:

-   -   (3-a) preparing a fiber sheet of discontinuous reinforcing        fibers having a fiber length of 1 to 300 mm and arranged in one        direction, wherein the edges of the fibers having the fiber        length are located at different positions in the length        direction,    -   (3-b) forming a prepreg base by impregnating a matrix resin at        least partially into the fiber sheet prepared in the step (3-a),        and    -   (3-c) forming an additional resin layer on at least one of the        surfaces of the prepreg base formed in the step (3-b).

It is preferable in the composite prepreg base production processes thatthe cuts formed in the prepreg base comprises cuts having a length of 2to 50 mm arranged with an interval each other in cut-rows each of whichis directed to a direction across the direction of the arrangement ofthe reinforcing fibers and which are arranged with an interval eachother in the direction of the arrangement of the reinforcing fibers,wherein a distance between two cut-rows that are in such a relation thatwhen one of them is moved in the direction of the arrangement of thereinforcing fibers, each cut on it meets another on the other cut-row,is in the range of 10 to 100 mm; positions of the cuts in the adjacentcut-rows in the direction of the arrangement of the reinforcing fibersare shifted each other in the direction perpendicular to the directionof the arrangement of the reinforcing fibers; and when the cuts areprojected in the direction of the arrangement of the reinforcing fibers,position of the ends of cuts in the adjacent cut-rows in the directionof the arrangement of the reinforcing fibers are overlapped each otherwith an overlap in the range from 0.1 mm to 10% of the length of theshortest of the adjacent cuts in the direction perpendicular to thedirection of the arrangement of the reinforcing fibers.

In the composite prepreg base production processes, it is preferablethat the additional resin layer formed on at least one of the surfacesof the prepreg base covers the whole or a part of a surface of theprepreg base and a thickness of the additional resin layer formed is inthe range from the diameter of a single fiber in the reinforcing fibersconstituting the reinforcing fiber sheet to the 0.5 times of a thicknessof the raw prepreg base.

It is preferable in the composite prepreg base production process thatthe additional resin layer contains particulate or fibrous fillers.

It is preferable in the composite prepreg base production process that aresin constituting the additional resin layer differs from the matrixresin constituting the raw prepreg base, and the minimum viscosity ofthe resin constituting the additional resin layer, in the range fromroom temperature to the decomposition temperature, is lower than that ofthe matrix resin.

It is preferable in the composite prepreg base production process that aresin constituting the additional resin layer differs from the matrixresin constituting the raw prepreg base, and a fracture toughness of theresin constituting the additional resin layer is higher than that of thematrix resin.

It is preferable in the composite prepreg base production process thatthe matrix resin constituting the raw prepreg base is a thermosettingresin, and the resin constituting the additional resin layer is athermoplastic resin.

We still further provide a layered base comprising a plurality ofcomposite prepreg bases each of which is produced by a method forproducing a composite prepreg base according to any one of compositeprepreg base production processes, in which the composite prepreg basesare laminated so that the additional resin layer exists on at least oneof the surfaces of the composite prepreg base, and the adjacentcomposite prepreg bases are adhered at least partially to each other.

We yet further provide a layered base comprising a plurality oflaminated layers each of which is composed of a raw prepreg basecomprising a fiber sheet of discontinuous reinforcing fibers having afiber length of 1 to 300 mm and arranged in one direction and a matrixresin impregnated into the fiber sheet, wherein an additional resinlayer is provided on at least one of the outermost layers and in atleast one of interlayer spaces of the laminated layers, and at theinterlayer spaces of the laminated layers, the raw prepreg bases eachother and/or the raw prepreg base and the additional resin layer areadhered at least partially at the interface between them to beintegrated each other.

In the layered base, it is preferable that thicknesses of the additionalresin layers on at least two composite prepreg bases in the plurality ofcomposite prepreg bases laminated each other are different each other.

It is preferable in the layered base that a thickness of the additionalresin layer on a surface of the layered base is larger than that of theadditional resin layer inside the layered base.

It is preferable in the layered base that the matrix resin thatconstitutes the raw prepreg base is a thermosetting resin, and a resinthat constitutes the additional resin layer is a thermoplastic resinwhich exposes on a surface of the layered base.

We yet further provide a fiber reinforced plastic produced by heatingand pressing the layered base, wherein an additional resin layer existson at least one of the surfaces of the layered base.

It is preferable in the fiber reinforced plastic that a resin thatconstitutes the additional resin layer exists between the ends ofadjacent of the discontinuous fibers of the reinforcing fibers.

A composite prepreg base production process serves to form an additionalresin layer on at least one of the surfaces of a raw prepreg base thatcomprises a fiber sheet of discontinuous reinforcing fibers having afiber length of 1 to 300 mm oriented in one direction and a matrix resinimpregnated into the fiber sheet. In a process to produce a moldedproduct by heating and pressing the composite prepreg base producedabove or a layered base produced by laminating the composite prepregbases, the additional resin layer serves to facilitate an alteration ofa position or shape of the composite prepreg base and/or the layeredbase.

Since the additional resin layer and the raw prepreg base are preparedseparately, a resin to be used to form the additional resin layer can beselected relatively unrestrictedly based on considerations of productionconditions for an intended molded product and flow state of the fibersduring the production process without significant restrictions relatingto the matrix resin used in the raw prepreg base. This allows goodflowability of the composite prepreg base and/or the layered base duringthe production of the intended molded product, high moldability into theintended product shape, and a wide range of production conditions forthe intended product. Furthermore, this makes it possible to produce afiber reinforced plastic having good mechanical properties, high qualitystability and good appearance quality.

The resulting fiber reinforced plastics can be used effectively asmaterial for structural elements that have a complicated shapecontaining ribs and quadric surfaces, such as those of transportequipment (automobile, aircraft, naval vessels etc.), industrialmachines, precision equipment and sports equipment (bicycle, golfoutfit, etc.).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic cross section of a layered base laminated witha plurality of composite prepreg bases (four bases are shown in thefigure) produced by a composite prepreg base production process.

FIG. 2 shows a schematic cross section of an FRP produced from thelayered base illustrated in FIG. 1.

FIG. 3 shows a schematic plan view of an example of a raw prepreg baseused for a composite prepreg base production process.

FIG. 4 shows a schematic cross section of a layered base laminated withconventional prepreg bases (four bases are shown in the figure).

FIG. 5 shows a schematic cross section of a conventional FRP producedfrom the layered base illustrated in FIG. 4.

REFERENCE NUMBERS LIST

-   -   1: the direction of the arrangement of reinforcing fibers    -   2: the direction across the direction of the arrangement of        reinforcing fibers    -   3: reinforcing fibers    -   4: an end of discontinuous reinforcing fibers    -   5: a width of overlap between cuts in adjacent cut-rows when the        cuts are projected in the direction of the arrangement of the        reinforcing fibers    -   6: a fiber length of discontinuous fibers    -   7: a cut-row of cuts    -   7 a, 7 b: cuts    -   8: a cut-row of cuts    -   8 a, 8 b, 8 c: cuts    -   9: a cut-row of cuts    -   9 a, 9 b: cuts    -   10, 10 a, 10 b, 10 c, 10 d: an additional resin layer    -   11, 11 a, 11 b, 11 c: an interlayer space    -   12: the lower mold in a mold    -   13: an interval between the ends of adjacent discontinuous        reinforcing fibers    -   13 a: a gap between the ends of adjacent discontinuous        reinforcing fibers    -   14: a void    -   15: a resin that has flowed into a gap between the ends of        adjacent discontinuous reinforcing fibers    -   30: a fiber sheet    -   40: a plurality of cuts, or an individual cut    -   50: a plurality of cut-rows of cuts, or an individual cut-row of        cuts    -   a: a composite prepreg base    -   a′: a raw prepreg base    -   b: a layered base    -   c: an FRP    -   d: a conventional layered base    -   e: a conventional FRP

DETAILED DESCRIPTION

The term “a raw prepreg base” as used in this specification refers to aprepreg base composed of a fiber sheet of discontinuous reinforcingfibers having a fiber length of 1 to 300 mm arranged in one directionand a matrix resin impregnated into the fiber sheet. A composite prepregbase produced based on a method for producing a composite prepreg basediffers from the raw prepreg base in that an additional resin layer isprovided on at least one of the surfaces of the raw prepreg base. Theterm “fiber sheet” refers to a sheet in which a plurality of fibersarranged in a form of sheet-like or tape-like free from impregnation ofa resin which is widely used in a conventional prepreg or a productionthereof. The plurality of fibers is usually arranged with impregnationof a matrix resin which is coated on a release paper having a form ofsheet-like or tape-like.

In the fiber sheet, the whole of the plurality of arranged fibers may becompletely impregnated with the matrix resin or a part of the pluralityof arranged fibers may be partially impregnated with the matrix resin. Acomplete impregnation with the matrix resin serves effectively to reducea fraction of voids in an FRP produced by molding the composite prepregbase, and therefore, the raw prepreg base comprising the fiber sheetimpregnated substantially completely with the matrix resin are usedpreferably for implementing this disclosure.

“Substantially complete impregnation” as referred to herein is definednormally as a state in which a void fraction is in 2% or less. “Partialimpregnation” is defined normally as a state in which a void fraction ismore than 2% or a state free of voids but containing dry parts (partsfree of adhesive) in the arranged fibers (i.e., a state of a semipreg).Further, the term “fiber” and term including “fiber” (such as “adirection of fiber”) refers to a reinforcing fiber, unless otherwisedefined.

FIG. 1 shows a schematic cross section of a layered base b obtained bylaminating four composite prepreg bases each of which was produced by amethod for producing a composite prepreg base. In FIG. 1, the layeredbase b is produced by laminating four composite prepreg bases a, withthe lamination directions (fibers arrangement directions) being shiftedwith 90° each other. The layered base b is placed on the upper face of alower mold 12. In FIG. 1, a raw prepreg base a′ in each of second andfourth layers has ends 4 of discontinuous reinforcing fibers 3 formed bycuts in the central region. Additional resin layers 10 a, 10 b, 10 c and10 d are located in the interlayer spaces 11 a, 11 b and 11 c, andbetween the fourth layer counted from the top and the lower mold 12.Hereinafter, each of these interlayer spaces and each of theseadditional resin layers will be referred to as an interlayer space 11and an additional resin layer 12, respectively, without consideration oftheir positions.

FIG. 2 shows a schematic cross section of an FRP c produced from thelayered base b illustrated in FIG. 1. The FRP c is formed by applying apressing pressure from above onto the layered base b in FIG. 1. In FIG.2, the second and fourth layers counted from the top are divided in thecentral region into the right and left hands, and the ends 4 of thediscontinuous reinforcing fibers 3, which are in contact with each otherin the case of the layered base b in FIG. 1, are separated with aninterval 13 to form a gap 13 a. In FIG. 2, the additional resin layers10 a, 10 b, 10 c and 10 d, which are located in the interlayer spaces 11a, 11 b and 11 c, and between the fourth layer and the lower mold 12 inFIG. 1, are extended thinly between the layers and over the surface inthe FRP c, and flow into the gap 13 a that is formed in the interval 13between the ends 4 of the adjacent discontinuous reinforcing fibers,filling the gap 13 a as resin 15.

FIG. 4 shows a schematic cross section of a layered base d obtained bylaminating four conventional prepreg bases a′. Each of the conventionalprepreg bases a′ is the same to the raw prepreg base a′ shown in FIG. 1,and therefore, they are represented by the same sign a′. In FIG. 4, thelayered base d is formed by laminating four prepreg bases a′, with thelamination directions (fibers arrangement directions) being shifted with90° each other. In FIG. 4, the prepreg bases a′ in the second and fourthlayers counted from the top contain ends 4 of discontinuous reinforcingfibers 3 formed by cuts in the central region.

FIG. 5 shows a schematic cross section of a conventional FRP e producedfrom the layered base d illustrated in FIG. 4. The FRP e is produced byapplying a pressing pressure from above onto the layered base d in FIG.4. In FIG. 5, the second and fourth layers counted from the top aredivided in the central region into the right and left hands, and theends 4 of the discontinuous reinforcing fibers, which are in contactwith each other in the case of the layered base d in FIG. 4, areseparated with an interval 13 to form a gap 13 a. A matrix resinsqueezed out from each of the layers or adjacent layers enter the gap 13a that is formed in the interval 13 between the ends 4 of adjacent thediscontinuous reinforcing fibers. However, the quantity of resin thatcan enter the gap 13 a is small, leading to formation of voids in thegap 13 a.

The composite prepreg base a produced by a method for producing acomposite prepreg base comprises discontinuous reinforcing fibers 3arranged in one direction, and a laminar resin layer, i.e., theadditional resin layer 10, formed on at least one of the surfaces of theraw prepreg base a′. This configuration serves to achieve the followingeffects.

First, the reinforcing fibers 3 are arranged in one direction, and thisarrangement direction of the reinforcing fibers 3 can be controlled byadjusting the arrangement direction of the composite prepreg base aduring the lamination step. The use of a composite prepreg base acomprising reinforcing fibers oriented in one direction, therefore,makes it possible to design an FRP having desired mechanical propertiesand produce an FRP having high quality stability (first effect).

Second, the reinforcing fibers 3 are discontinuous, and this allows thecomposite prepreg base a to flow in the orientation direction of thereinforcing fibers 3 during the FRP molding process. In FIG. 1, a layercomprising the raw prepreg base a′ is extended in the width direction(right to left direction in the case of the first and third layerscounted from the top) of the reinforcing fibers 3. At the same time, asthe interval 13 between the ends 4 of adjacent discontinuous fibers isextended, the entire composite prepreg base a is also extend in thefiber direction (right to left direction in the case of the second andfourth layers counted from the top) of the reinforcing fibers 3, leadingto good molding properties (high flowability, shape followingcharacteristics and wide range of effective molding conditions) (secondeffect).

If the reinforcing fibers 3 are entirely continuous fibers, on the otherhand, the composite prepreg base a will not be able to flow in the fiberarrangement direction, making it impossible to produce an FRP in acomplicated shape.

In the discontinuous reinforcing fibers 3, the fibers in the compositeprepreg base a has a finite length, which means that the length of thereinforcing fibers 3 is smaller than the total length of the compositeprepreg base a in the fiber arrangement direction of the compositeprepreg base a. Specifically, the fiber length in the reinforcing fibers3 is in the range of 1 to 300 mm. The fiber length should preferably bein the range of 10 to 100 mm, more preferably 5 to 30 mm. If the fiberlength is less than 1 mm, the orientation of the reinforcing fibers willtend to deteriorate while flowing during the molding process, sometimesleading to a large deterioration in the mechanical properties.

If the fiber length is larger than 300 mm, on the other hand, the fiberlength will be too large and the reinforcing fibers will tend todeteriorate in flowability, leading to a large variation in mechanicalproperties. If the fiber length is in the aforementioned range, however,the reinforcing fibers will be able to serve to achieve the desiredreinforcing effect even if the reinforcing fibers in the FRP arediscontinuous. Specific examples of reinforcing fibers that arediscontinuous and oriented in one direction are described later.

Third, the laminar additional resin layer 10 provided on at least one ofthe surfaces of the raw prepreg base a′ in the composite prepreg base aserves to achieve very good molding characteristics (third effect).

One of the features is that this effect is found to be enhanced verylargely as a result of working in synergy with the second effect. If thereinforcing fibers 3 are discontinuous, it is not enough to allow theentire an raw prepreg base a′ to be extended sufficiently during an FRPmolding process. We found that the molding characteristics of thelayered base b and the layered base d produced by laminating two or moreraw prepreg bases a′ depend largely not only on the extension of theentire the raw prepreg base a′ alone but also on the interaction(friction resistance at the interfaces 11 a, 11 b and 11 c) betweenadjacent the laminated prepreg bases, and this finding led to thelayered base b. comprising two or more laminated composite prepreg basesa.

In FIG. 1, when a pressing pressure is applied to the layered base bfrom above in the downward direction, each layer becomes thinner, andthe raw prepreg base a′ is extended in the width direction of thereinforcing fibers 3 (the horizontal direction in the first and thirdlayers, counted from the top). The difference in extension degree,acting as shearing force, is transmitted through the interfaces 11 a, 11b and 11 c to apply a load in the fiber direction of the reinforcingfibers 3 (the horizontal direction in the second and fourth layers,counted from the top).

As shown FIG. 2, the second and fourth layers are divided by this loadin the central region into two in the horizontal direction, and the ends4 of the adjacent discontinuous reinforcing fibers, which are in contactwith each other in the case of the layered base b illustrated in FIG. 1,are separated with an interval 13. in particular, when a mold composedof the lower mold 12 and a upper mold is used for press molding toproduce an FRP, the friction resistance between the raw prepreg base a′and the lower mold 12 also has large influence in addition to the abovefactors. The additional resin layers 10 a, 10 b, 10 c and 10 d locatedat the interface 11 and between the raw prepreg base a′ and the lowermold 12 facilitate slippage of the raw prepreg base a′ during the FRPmolding process, leading to an increased flowability.

A very high flowability, shape followability and a wide range of moldingconditions are realized by a synergistic effect based on thetwo-dimensional extension of the entire raw prepreg base a′, and theinteraction between adjacent composite prepreg bases a and between thecomposite prepreg base a and the mold.

The additional resin layer 10 that has effects as described above may beformed on either one or both of the surfaces of the raw prepreg base a′.The former may be preferable if the additional resin layer has to beintroduced at low costs, while the latter is preferable if both surfacesof the composite prepreg base are equally used, without proper use eachother. It is more preferable to provide the layer on both surfacesbecause larger effects can be achieved.

In addition to the aforementioned effect, the use of the additionalresin layer 10 serves to produce an FRP having well appearance qualityand to bring effect of lessening voids (fourth effect).

When the interval 13 between the ends 4 of adjacent discontinuous fibersis widened to two-dimensionally extend the entire an raw prepreg base a′as shown in FIG. 5, the matrix resin would not normally be expected toexist in the gap 13 a in the reinforcing fibers 13 that results from theincreased interval 13 between the ends 4 of adjacent discontinuousfibers. Thus, the matrix resin will be squeezed out of other portionsinto the gap 13 a, or the adjacent layer will move to fill the gap 13 a.

However, it is not easy to squeeze out the matrix resin into the gap 13a or move the adjacent layers into it, and in conventional a prepregbases (for instance, the raw prepreg base described in JP 63-247012 A),therefore, the gap 13 a is not easily filled with the resinsufficiently, and voids 14 tend to be formed in the gap 13 a. If suchvoids 14 exist in the surface of the molded FRP, they not only lead tothe FRP with heavily poor appearance quality, but also cause stressconcentration in the portions containing the voids 14 when a load isapplied to the FRP, resulting in fatal defects such as deterioration inthe mechanical characteristics of the FRP. If the adjacent layers enterthe gap 13 a, on the other hand, the laminated layers will sufferundulations, leading to deterioration in the physical properties of theFRP.

Compared to this, if the additional resin layer 10 is formed on at leastone of the surfaces of the raw prepreg base a′ as shown in FIG. 2, theresin in the additional resin layer 10 will be supplied to (flow into)the gap 13 a that results from an increase in the interval 13 betweenthe ends 4 of adjacent discontinuous reinforcing fibers 3, to completelyprevent the formation of voids 14 such as illustrated in FIG. 5. Thus,the additional resin layer 10, in place of the matrix resin, acts as thesupply source of resin to prevent the formation of the voids 14. This isbecause causing the resin constituting the additional resin layer toflow is much easier than squeezing out the matrix resin. The findingthat such an additional resin layer can serve very effectively forimprovement in appearance quality of an FRP and reduction of voids inthe FRP is also one of the advantageous features.

Other notable effects include, in particular, the improvement of anFRP's tensile strength that can be achieved by the use of such anadditional resin layer (fifth effect). Since the composite prepreg basea is composed of discontinuous reinforcing fibers 3, destruction isnormally expected to start at the ends 4 of the discontinuous fiberswhere the reinforcing fibers 3 are separated. Conventionally, therefore,such products tend to be low in tensile strength compared to thosecomprising continuous reinforcing fibers.

On the other hand, if the additional resin layer has a high fracturetoughness (Mode I fracture toughness G_(IC) of a resin itselfconstituting the additional resin layer, Mode II fracture toughnessG_(IIC) of an FRP produced from the composite prepreg base comprisingthe additional resin layer), in particular, it acts to minimize thegeneration and expansion of initial cracks that can occur at the ends ofsevered reinforcing fibers and/or, even if initial cracks have takenplace, it serves to reduce the progress of separation of interfaces thatconnect the ends of discontinuous reinforcing fibers with the ends ofother discontinuous reinforcing fibers (such as those in the adjacentlayers). Therefore, the destruction starting at the ends of thediscontinuous reinforcing fibers can be minimized by using theadditional resin layer that comprises resin having appropriate fracturetoughness. As a result, it becomes possible to allow the FRP to have ahigher tensile strength. The finding that the use of the additionalresin layer serves very effectively to improve the tensile strength isalso one of the advantageous features.

The resin used in the additional resin layer may be the same as thematrix resin. From the viewpoint of the compatibility between theadditional resin layer and the matrix resin, the selection of anappropriate resin composition for a composite prepreg base can besimplified, making it possible to streamline the production process.

On the other hand, the aforementioned third and fourth effects aremaximized if the additional resin layer comprises a resin that is lowerthan the matrix resin in the minimum viscosity in the range from roomtemperature to the decomposition temperature (hereinafter, simplyreferred to as minimum viscosity). If the matrix resin in the rawprepreg base is a thermosetting resin, the range from room temperatureto its decomposition temperature is normally from about 80° C. to about150° C. The use of an additional resin layer that comprises a resinhaving a lower viscosity than the matrix resin serves to achieve one ofthe most preferable examples.

Specifically, it is preferable that the minimum viscosity of the resinconstituting the additional resin layer is ⅘ or less of that of thematrix resin. It should more preferably be ⅔ or less, still morepreferably ½ or less. If the minimum viscosity is too low, theadditional resin layer will possibly flow out, failing to achieve thethird and fourth effects.

From this viewpoint, the minimum viscosity should preferably be 1/500 ormore of the matrix resin. It should more preferably be 1/100 or more. Asa matter of course, when selecting a resin to be used to constitute theadditional resin layer, its adhesiveness and compatibility with thematrix resin should be examined, and for instance, a combination of ahigh-viscosity resin with a low-viscosity one of the same resin speciesis preferable. If the viscosity of the matrix resin is sufficiently low,however, it is not necessary for the viscosity of the additional resinlayer to be lower than that of the matrix resin, and even if it ishigher than the viscosity of the matrix resin, it will be highlypossible to achieve the effect.

The minimum viscosity of a resin is determined from curves showing therelation between a temperature and a viscosity in the range from roomtemperature to a decomposition temperature of a resin under theconditions of a. heating rate of 2° C./min, a vibration frequency of 0.5Hz, and use of parallel plates (diameter 40 mm). The measuring equipmentwas an expansion-type ARES viscoelasticity measuring system supplied byRheometric Scientific Inc. The decomposition temperature of the resin isdetermined with the thermogravimetric (TG) analysis method where theresin was heated in a nitrogen atmosphere at a rate of 10° C./min todetermine the temperature at which the thermal weight loss reaches 30%.

From another viewpoint, the fifth effect can be maximized if the resinconstituting the additional resin layer has a higher fracture toughness(Mode I fracture toughness G_(IC) of a resin itself constituting theadditional resin layer, and Mode II fracture toughness G_(IIC) of an FRPproduced from the composite prepreg base comprising the additional resinlayer) than that of the matrix resin. The use of an additional resinlayer comprising a resin having a higher fracture toughness than that ofthe matrix resin serves to achieve one of the most preferable examples.For instance, such a relation can be achieved by using a combination ofa high-ductility resin with a low-ductility one of the same resinspecies, or a combination of an additional resin layer containing afiller as described later and a matrix resin free of fillers.

If the fracture toughness of the matrix resin is sufficiently high, itis not necessary for the resin constituting the additional resin layerto have a very high fracture toughness, but the effect can be achievedto a sufficient degree even if its fracture toughness is lower than thatof the matrix resin. From this viewpoint, the Mode I fracture toughnessG_(IC) of the resin constituting the additional resin layer shouldpreferably be 150 J/m² or more, more preferably 250 J/m² or more, stillmore preferably 450 J/m² or more. There are no specific upper limits tothe fracture toughness G_(IC) when considered separately, meaning thatthe higher the better. In general, however, the fracture toughnessG_(IC) is in a trade-off relation with the heat resistance, and fromthis viewpoint, it is preferable that the fracture toughness G_(IC)should preferably be 1 kJ/m² or less to maintain a heat resistance of100° C. or more.

For FRP produced from a composite prepreg base comprising an additionalresin layer, the fracture toughness G_(IIC) of the Mode II shouldpreferably be 1 kJ/m² or more, more preferably 1.5 kJ/m² or more, andstill more preferably 2 kJ/m² or more. There are no specific upperlimits to the fracture toughness G_(IIC) when considered separately,meaning that the higher the better. In general, however, the fracturetoughness G_(IIC) is in a trade-off relation with the heat resistance,and from this viewpoint, it is preferable that the fracture toughnessG_(IIC) should preferably be 5 kJ/m² or less to maintain a heatresistance of 100° C. or more.

The fracture toughness G_(IC) of resin was calculated by the followingprocedure. Plates of cured resin (2±0.1 mm thickness, 10±0.5 mm width,120±10 mm length) were used as test pieces. The tensile modulus E andPoisson's ratio v of these test pieces were measured according to themethod described in JIS K7161-1994 “Plastics—tensile characteristicstest method.” Similarly, K_(IC) of plates of heat-cured resin (6±0.3 mmthickness, 12.7±0.3 mm width, 80±10 mm length) was measured according toASTM D5045-99. The fracture toughness G_(IC) was calculated from thetensile modulus E, Poisson's ratio υ, and K_(IC) by the formula((1−υ)²×K_(IC) ²)/E. The number n of measurements made was 10 times. Thefracture toughness G_(IIC) of an FRP was determined based on ENF test(flexure test for end-notched test pieces) according to the methoddescribed in Appendix 2 to JIS K7086-1993 “Interlaminar fracturetoughness test method for carbon fiber reinforced plastics.” The numbern of measurements made was 10 times.

The additional resin layer may cover the entire surface of the rawprepreg base, or may cover a part of the surface of the raw prepregbase. The additional resin layer covering the entire surface may, forinstance, be in a form of resin film. The additional resin layercovering a part of the surface may, for instance, be in a form offibrous material comprising a resin (such as nonwoven fabric, mat, net,mesh, woven fabric, knitted fabric, short fiber bundles, and continuousfiber bundles) or aggregates of particulate material composed ofresin-based particles in a dispersed state.

The additional resin layer should preferably be such that the third orfourth effects are achieved to the highest possible degree. Inparticular, a resin film is preferable because these effects can beachieved economically and most effectively. A resin constituting theadditional resin layer may be in a form of aggregates of particles whenan FRP having a high content of reinforcing fibers is to be produced. Inthe case of aggregates of particles, it is possible not only to use aresin that is difficult to process into film, but also to largely reducethe quantity of resin required to form an intended additional resinlayer.

When using particles, the average diameter of the particles shouldpreferably be 1 mm or less, more preferably 250 μm or less, and stillmore preferably 50 μm or less, because the particles having a smalleraverage diameter (minor axis in the case of ellipsoidal particles) canbe dispersed more uniformly over a surface of the raw prepreg base. Theeffect will level off as the particle size becomes extremely small, andfrom this viewpoint, the minimum required average particle diameter is 1μm or more.

The thickness of the additional resin layer should preferably be in therange from the diameter of a single fiber in the reinforcing fibers tothe 0.5 times of the thickness of the raw prepreg base. If the thicknessof the additional resin layer is smaller than the diameter of the singlefiber in the reinforcing fibers, the interface friction resistance willnot be sufficiently high, sometimes failing to prevent the improvementin molding characteristics. If the thickness of the additional resinlayer is larger than the 0.5 times of the thickness of the raw prepregbase, the fiber content of an FRP will be too small, sometimes failingto achieve a sufficient weight reduction. Specifically, if thereinforcing fibers are carbon fibers and the thickness of the rawprepreg base is in the common range of 0.1 to 0.6 mm, the thickness ofthe additional resin layer should preferably be in the range of 5 to 300μm. It should more preferably be in the range of 10 to 80 μm, still morepreferably 15 to 60 μm.

The thickness of the additional resin layer is determined by observingthe cross section of the composite prepreg base with an opticalmicroscope, measuring the height (thickness) at randomly selected 20points, and averaging the measurements. If the resin that constitutesthe additional resin layer is in the form of aggregates of fibrous orparticulate material, 20 highest points where the resin forms domainsshould be selected randomly.

If the additional resin layer is in the form of a film layer, inparticular, it is preferable that the additional resin layer contains afiller. Such a filler may be in the form of, for instance, particles(ellipse, sphere, perfect sphere, etc.), flakes, scales, ordiscontinuous short fibers (chopped fiber, milled fiber). If theadditional resin layer is in the form of a film layer, in particular,the filler to be used may be in the form of fibrous sheet (nonwovenfabric, mat, net, mesh, woven fabric, knitted fabric, continuous fiberbundles, etc.).

If such a filler is contained, it acts like a log or roller used to movea heavy object (bearing effect) to largely reduce the frictionresistance between adjacent a composite prepreg base layers or betweenthe composite prepreg base and the mold, serving to further enhance thethird or fourth effects. From this viewpoint, the filler should morepreferably be spherical or perfectly spherical, and it is particularlypreferable that they are in the form of hollow spheres to producelightweight products. Specifically, the filler may be in the form ofinorganic particles (particles of glass, carbon, mica, etc.), or resinparticles (particles of phenol, polyamide, epoxy resin, etc.).

If a filler that improves the fracture toughness of the additional resinlayer itself is contained in the additional resin layer, it works toreduce the energy transfer/absorption and crack generation/expansionwhen an impact or a load is applied to the FRP. As a result, it preventsdestruction at the interface between he composite prepreg bases toenhance the fifth effect.

From this viewpoint, the filler should preferably have a higher fracturetoughness than the that of the resin constituting the additional resinlayer and the matrix resin. Specifically, preferable materials includeresin particles (particles of polyamide (particularly, polyamide 12),polyether sulfone, polyetherimide, polyamide-imide, polyether etherketone, polyketone resin, etc.).

The use of such resin particles allows the fracture toughness G_(IC) ofMode I of the resin itself that constitutes the additional resin layerto be easily adjusted in the aforementioned range and to be increasedthe preferable range of 150 J/m² or more, and to the more preferablerange of 250 J/m² or more. If greater importance is placed on theprevention of destruction at the interface between the composite prepregbases rather than flowability, it is particularly preferable that theadditional resin layer is in the form of a fibrous sheet (particularly,nonwoven fabric) because it serves to enhance the effect.

There are three typical examples of fiber sheets of reinforcing fibersthat are discontinuous and oriented in one direction.

-   -   Example A: a sheet or tape of discontinuous reinforcing fibers        produced by an appropriate spinning means such as a draft zone        system spinning.    -   Example B: a sheet or tape of discontinuous reinforcing fibers        (for instance, chopped fibers) oriented in one direction.    -   Example C: a fiber sheet produced by forming cuts having        finite-length into a fiber sheet comprising continuous        reinforcing fibers in which the cuts are provided on all over        the fiber sheet in a direction across the reinforcing fibers.

According to Example A, it is able to form a fiber sheet having ends ofsingle fibers in discontinuous reinforcing fibers each of which ends isnot aligned and randomly arranged with each other, and therefore, themolding characteristics are slightly inferior, but very good mechanicalcharacteristics and high quality stability can be achieved.

According to Example B, it is able to form a fiber sheet having ends ofsingle fibers in discontinuous reinforcing fibers a plural of which endsare aligned and arranged somewhat regularly with each other, andtherefore the quality stability is slightly inferior, but very goodmolding characteristics can be achieved.

According to Example C, it is able to form a fiber sheet having ends ofsingle fibers in discontinuous reinforcing fibers a plural of which endsare aligned and arranged regularly, and therefore, good mechanicalcharacteristics, high quality stability and good molding characteristicsare all achieved in good balance.

Any of the aforementioned examples may be used to meet specificpurposes, but Example C can be said to be the most preferable becausemechanical characteristics and molding characteristics can be developedin good balance and its production is easy to perform. Thus, Example Cis described in detail below with reference to drawings.

FIG. 3 shows a schematic plan view of an example of the compositeprepreg base a produced based on Example C. FIG. 3 illustrates a typicalcut arrangement pattern formed with many cuts 40 provided in manycontinuous reinforcing fibers 3 at intervals in a direction 2 across afiber orientation direction 1 and the fiber orientation direction 1 in afiber sheet 30 which comprises the many continuous reinforcing fibers 3arranged in the fiber orientation direction 1, i.e., the top-bottomdirection (longitudinal direction) in the figure. The many cuts 40 areformed with cut-rows 50 each of which consists of a plurality of cuts,arranged in the direction 2 across the fiber orientation direction 1 ofthe reinforcing fibers 3 at intervals as well as arranged in the fiberorientation direction 1 of the reinforcing fibers 3 at intervals.

Referring to FIG. 3 for detailed description, many cuts 40 are composedof a cut-row 7 comprising a plurality of cuts 7 a and 7 b aligned atintervals along the horizontal direction 2, a cut-row 8 comprising aplurality of cuts 8 a, 8 b and 8 c aligned at intervals along thehorizontal direction 2, and a cut-row 9 comprising a plurality of cuts 9a and 9 b aligned at intervals along the horizontal direction 2. Manycut-rows 50 are formed with a plurality of cut-rows 7, 8 and 9. In oneof the cut-rows 50, a required number of cuts 40 are aligned in thewidth direction of the fiber sheet 30, or are aligned over the entirewidth of the fiber sheet 30. A required number of cut-rows 50 are alsoaligned in the length direction of the fiber sheet 30, or are alignedover the entire length of the fiber sheet 30.

The relation between FIGS. 1 and 3 can be understood easily if attentionis given to the fiber orientation direction of the reinforcing fibers 3shown in the figures, and the plan view of the composite prepreg base ain FIG. 3 is assumed to be the plan view of the top layer that comprisesthe composite prepreg base a or the third layer (counted from the top)that comprises the composite prepreg base a in FIG. 3. The additionalresin layer 10 is not included in FIG. 3 because it is located under thefiber sheet 30. Moreover, the matrix resin impregnated in the fibersheet 30 is not shown either. The many cuts 40 and its arrangementpattern should preferably be as described in the following example.

Each of the cuts 40 put at intervals along each of the cut-rows 50should preferably have a length of 2 to 50 mm. When a cut-row (forinstance, the cut-row 7) is moved in the fiber orientation direction 1of the reinforcing fibers 3 until the cuts on the cut-row first overlapthose on another cut-row (for instance, the cut-row 9), the distancebetween the two cut-rows, i.e., the fiber length 6 of the reinforcingfibers 3 cut at the higher and lower ends by cuts (for instance, thecuts 7 a and 9 a), should preferably be in the range of 1 to 300 mm.

It is preferable that the positions of cuts (for instance, the cuts 7 aand 8 a) on two adjacent cut-rows (for instance, the cut-rows 7 and 8)are shifted in the perpendicular direction to the fiber orientationdirection 1 of the reinforcing fibers 3, and that, when projectedthrough in the fiber orientation direction 1 of the reinforcing fibers3, cuts (for instance, the cuts 7 a and 8 a) on two adjacent cut-rows(for instance, the cut-rows 7 and 8) have an overlap with a length 5.The existence of this overlap with a length 5 allows the reinforcingfibers 3 to comprise bundles of many discontinuous fibers that are notcontinuous in the length direction (the fiber orientation direction 1)and have a prescribed length, for instance, a length in the range of 1to 300 mm.

The composite prepreg base a shown in FIG. 3 has a pattern of cuts thatcomprises two types of cut-rows (for instance, the cut-rows 7 and 8)with cuts 40 in the same shape and direction, i.e., cuts 40 aligned inthe perpendicular direction 2 to the orientation direction 1 of thereinforcing fibers 3, but there are no limitations on the pattern ofcuts if the reinforcing fibers 3 are divided by cuts 40 intodiscontinuous bundles. If the cuts on two adjacent cut-rows are notshifted in the perpendicular direction 2 to the orientation direction 1of the reinforcing fibers, some of the reinforcing fibers will be leftuncut, sometimes leading to a large decrease in flowability.

In the composite prepreg base a shown in FIG. 3, it is preferable thatthe overlap length 5 in the overlaps between the cuts on two adjacentcut-rows should preferably be 0.1 mm or more, and smaller than 10% ofthe length of the shortest among the adjacent cuts in the same cut-row.An overlap length 5 of less than 0.1 mm is not preferable becausereinforcing fibers that are left uncut and longer than the intendedfiber length can be included, and such fibers will work to largelydecrease the flowability. If the overlap length 5 of cuts is larger than10% of the length of the shortest among the adjacent cuts, the ratiobetween the number of the fibers divided by a cut and that of the fibersamong them that are divided by a cut on the adjacent cut-row, i.e., theproportion of the fibers shorter than the intended fiber length, willincrease, leading to a molded FRP products having heavily poormechanical properties, and therefore, it is not preferable. If some cutslocated at the edge of the composite prepreg base do not have a fulllength, they are included in the shortest among the adjacent cuts, andin such a case, the inner cuts next to them are considered.

When the composite prepreg base a is produced according to Example C, itis preferable that all of the cuts 40 are in the same shape, size anddirection. The effect can be achieved if there are two or more types ofcuts 40 that are in different shapes, sizes or directions, fibers canflow uniformly and the flow of the fibers can be controlled easily whenall of the fibers have the same features. As a result, this prevents thegeneration of warp in a molded FRP, and the control of the fiberorientations, i.e., appropriate setting of the fiber directions in aplurality of layers of laminated composite prepreg bases makes itpossible to design an FRP product having desired mechanical properties.

When the composite prepreg base a is produced according to Example C, itis preferable that the cuts 40 are distributed consecutively at regularintervals in the perpendicular direction to the fibers. As in the caseof the aforementioned shape, size and direction of cuts, fibers locatedat regular intervals will flow uniformly, allowing easy control of theflowability of fibers. As a result, this prevents the generation of warpin a molded FRP, and the control of the fiber orientations makes itpossible to design an FRP product having desired mechanical properties.

When the composite prepreg base a is produced according to Example C,the shape of the cuts may be straight, curved, a combination of straightsegments, or a combination of straight and curved segments. In the caseof straight cuts, their directions may be diagonal or perpendicular tothe fiber direction.

If a film-like additional resin layer is used in the composite prepregbase a produced according to Example C, in particular, it is preferablethat the additional resin layer also have cuts at the same positions asthose in the reinforcing fibers. Such cuts located at the same positionsserves to allow the additional resin layer and the reinforcing fibers toflow harmoniously. Formation of cuts can allow air to gain in the rawprepreg base, but if the additional resin layer has cuts at the samepositions, air in the raw prepreg base will be easily come out,preventing the formation of voids in a molded FRP product, which is alsoan advantage.

If the additional resin layer comprises aggregates of fibrous orparticulate material, instead of film, the additional resin layer willbe permeable to air, and therefore, the air contained in the raw prepregbase as a result of the formation of cuts can easily come out if theadditional resin layer is free of cuts at the same positions as those inthe raw prepreg base. Rather, it is preferable that the additional resinlayer is free of cuts. If the additional resin layer is free of cuts andcomprises continuous fibers, it will serve to prevent initial cracksfrom being formed in the portions where reinforcing fibers are dividedby the cuts in the raw prepreg base, and minimize the expansion ofinitial cracks if they are formed. Even if initial cracks are formed, itwill be possible to prevent interlaminar separation extending betweenthe ends of discontinuous reinforcing fibers in the portions where theinitial cracks are formed and the ends of other discontinuousreinforcing fibers, for instance, the ends of discontinuous reinforcingfibers in the adjacent layer. As a result, the fifth effect can bemaximized. Needless to say, no problems will cause by an cut-freeadditional resin layer if the raw prepreg base does not contain air as aresult of putting cuts in it.

When the composite prepreg base is produced according to Example A orExample B, on the other hand, the matrix resin may be impregnated in thediscontinuous reinforcing fibers in the raw prepreg base before thestart of a molding process. This eliminates the need for removing airthrough the additional resin layer or for putting cuts in the additionalresin layer at the same positions as the ends of the discontinuousreinforcing fibers, and it will be preferable the additional resin layerdoes not have cuts. If the additional resin layer contains no cuts andcomprises continuous fibers, the interaction (interface frictionresistance) between adjacent laminated composite prepreg bases can beminimized to maximize the third and fifth effects.

In the composite prepreg base, particularly the composite prepreg baseproduced according to Example C, it is preferable that the many orientedreinforcing fibers are in close contact with a surface of a tape-like orsheet-like support. Rolling up the composite prepreg base can causeadhesion between surfaces of the rolled-up a composite prepreg base tomake unrolling impossible, but this can be prevented by using a supportwith releasability, even if the matrix resin is a thermosetting resinhaving tackiness.

In particular, if the reinforcing fibers are divided by cuts as in thecase of the composite prepreg base produced according to Example C, thesupport serves to maintain the shape of the composite prepreg base andprevent the reinforcing fibers from being removed and becoming unkemptduring the shaping step in an FRP molding process. If the matrix resinis a thermosetting resin having tackiness, the adhesion of the supportcan be achieved by the self-adhesiveness of the matrix resin. If thematrix resin is a thermosetting resin free of tackiness, it is achievedby the self-adhesiveness of the additional resin layer.

Materials for such a tape-like or sheet-like support include, forinstance, paper such as kraft paper and release paper, resin film suchas polyethylene and polypropylene resin, and metal foil such as aluminumfoil, and furthermore, a surface of the support may carry a silicone- orfluorine-base mold releasing agent or metal deposited film to havereleasability for resin.

The composite prepreg base should preferably have a thickness of 0.03 to1 mm. The thickness should more preferably be 0.04 to 0.15 mm, stillmore preferably 0.05 to 0.12 mm, and still more preferably 0.06 to 0.10mm. If the thickness is less than 0.04 mm, the number of fibers dividedby a cut inevitably becomes small, and undulation of fibers tends toresults from the flow during a molding process. Furthermore, productionof an FRP component having a thickness of 2 mm, for instance, requires acomposite prepreg base composed of 100 or more laminated layers, whichis not preferable in terms of production efficiency. If the thicknessexceeds 1 mm, on the other hand, the layer will account for a largeproportion of the total thickness of the laminate, which causes a largeanisotropy, possibly leading to warp etc. of a molded component.

If the raw prepreg base is produced by preparing a prepreg base fromcontinuous reinforcing fibers, followed by putting finite-length cuts atintervals over its entire surface in a direction across the reinforcingfibers as in the case of the composite prepreg base produced accordingto Example C, the cuts will penetrate through the thickness of the rawprepreg base, and therefore, a thinner a prepreg base will be moreadvantageous in terms of mechanical characteristics (in particular,tensile strength). From this viewpoint, the weight per unit area of thereinforcing fibers in the composite prepreg base should preferably be inthe range of 30 to 300 g/m², more preferably 40 to 150 g/m², and stillmore preferably 60 to 100 g/m².

There are no specific limitations on the type of the reinforcing fibersused, and suitable materials include, for instance, carbon fiber, glassfiber, organic fiber (such as aramid fiber, poly(p-phenylenebenzobisoxazole) fiber, polyethylene fiber, and polyvinyl alcoholfiber), metal fiber, ceramic fiber, and combinations of these fibers.Among others, carbon fiber, particularly polyacrylonitrile-based(PAN-based) carbon fiber, is high in specific strength and specificmodulus, and also high in water absorption resistance and environmentalresistance, and therefore, it is preferred as reinforcing fiber forstructural elements of aircraft and automobiles that require highstrength.

There are no specific limitations on the matrix resin if it serves asthe raw prepreg base and can be molded into an FRP.

Suitable resins to be used to constitute the additional resin layerinclude thermoplastic resins, thermosetting resins, and theircombinations that are selected appropriately. Specifically, they includethe following.

If a thermoplastic resin is used as a resin constituting the additionalresin layer, suitable ones include, for instance, polyester,polyolefine, styrene-based resin, polyoxy methylene, polyamide,polyurethane, polyurea, polydicyclopentadiene, polycarbonate,polymethylene methacrylate, polyvinyl chloride, polyvinyl formal,polyphenylene sulfide, polyphenylen ether, polyetherimide, polysulfone,polyallylate, polyether sulfone, polyketone, polyether ketone, polyetherether ketone, polyether ketone ketone, polyallylate, polyether nitrile,polyimide, polyamide-imide, phenol, phenoxy, polytetrafluoroethylene,other fluorine-based resins, elastomer (preferably,butadiene-acrylonitrile, carboxylic acid or amine modification of theformer, fluoroelastomer, polysiloxane elastomer), rubber (such asbutadiene, styrene-butadiene, styrene-butadiene-styrene,styrene-isoprene-styrene, natural rubber), resin for RIM (such as thosecontaining catalysts to produce polyamide 6, polyamide 12, polyurethane,polyurea, or polydicyclopentadiene), cyclic oligomer (such as thosecontaining catalysts to produce polycarbonate resin, polybutyleneterephthalate resin, etc.), and other resins such as copolymer of theformer, modification of the former, and blend of two or more of theformer. Among them, particularly preferable are polyamide, polyester,polyolefine, polyvinyl formal, and polyphenylen sulfone, because of agood balance between resin characteristics and cost, and degree ofdesign freedom for resin viscosity.

If a thermosetting resin is used as a resin constituting the additionalresin layer, suitable ones include, for instance, epoxy, phenol,polybenzimidazole, benzoxazine, cyanate ester, unsaturated polyester,vinyl ester, urea, melamine, bismaleimide, acrylic, polyimide,polyamideimide, etc., and other resin such as copolymer of the former,modification of the former and blend of two or more of the former, andstill other resins containing elastomer component, rubber component,curing agent, cure accelerator, catalyst, etc. These resins shouldpreferably be have a viscosity of 1×10⁶ Pa·s or less at room temperature(25° C.), and if the viscosity is in this range, the resin can serve toproduce a composite prepreg base with intended tackiness and drapeproperty.

If a resin constituting the additional resin layer is a thermosettingresin, the composite prepreg base will have tackiness at roomtemperature. When laminating the bases, therefore, these bases areintegrated by adhesion, and they can be molded while maintaining anintended lamination composition, thus constituting a good example. Witha large degree of design freedom in terms of resin viscosity, theminimum viscosity can be easily met in carrying out viscosity design,making it possible to maximize the effect.

From the viewpoint described above, the resin that constitutes afilm-like additional resin layer should preferably be a resincomposition comprising a thermosetting or thermosetting resin as primarycomponent. Needless to say, the intended effect can also be achievedwhen the additional resin layer comprises aggregates of fibrous orparticulate material, though a film-like layer can maximize the effect.

If the resin that constitutes the additional resin layer isthermoplastic resin, on the other hand, a film-like additional resinlayer will not have tackiness at room temperature, and therefore, theaforementioned effect will not be achieved as in the case ofthermosetting resin. If comprising aggregates of fibrous or particulatematerial, the additional resin layer will have good features that arecharacteristic of thermoplastic resin, such as high ductility, highadhesiveness (thermoplasticity) and ability to form an FRP having highstrength.

The matrix resin should preferably be a thermosetting resin or a resincomposition comprising a thermosetting resin as primary component (whichhereinafter may be simply referred to as a thermosetting resin). Amatrix resin that is a thermosetting resin or a resin compositioncomprising a thermosetting resin as primary component will have gooddrape property at room temperature, and therefore, in cases where, forinstance, a complex-shaped mold having ribbed irregular-shaped portionsor quadric surfaces has to be used for a molding, preliminary shapingcan be easily performed to give a complex contour shape to the resinbefore the molding. Such preliminary shaping serves to increase themolding characteristics and makes flow control easier.

If the matrix resin is a thermoplastic resin, it will be difficult toperform preliminary shaping at room temperature. Thermosetting resinsgenerally have tackiness, and the overall shape can be maintained if allreinforcing fibers are divided by cuts, making it possible to easilyprevent reinforcing fibers from being removed and becoming unkemptduring shaping. The primary component as referred to herein is definedas the component that accounts for more than 50% of the composition.

In these thermosetting resins, epoxy is particularly preferable. Epoxy,when used as matrix resin, show high adhesiveness and can achieve strongadhesion and tackiness between bases, and furthermore, the matrix resincomprising epoxy will show particularly good high mechanicalcharacteristics.

If the matrix resin is a thermoplastic resin, on the other hand, thecomposite prepreg bases, when laminated, will easily slip on each otherto cause a shift between them during a molding process becausethermoplastic resins are generally free of tackiness at roomtemperature, resulting in an FRP products having a large variation infiber orientation. In particular, such a variation can be very large inFRP products of a complicated shape having irregular-shaped portions.

It is preferable that the matrix resin of the raw prepreg base is athermosetting resin while the additional resin layer comprises athermoplastic resin. FRP products having a largely improved strength canbe produced by using a thermosetting resin having high adhesiveness withreinforcing fibers, high dimensional stability, high heat resistance andcreep resistance as the matrix resin of the raw prepreg base thataccount for a large proportion of the total resin quantity whileproviding high-ductility thermoplastic resin as interlayers. If,thermoplastic resin in the form of fiber (such as nonwoven fabrics inparticular,) or particles is used as the additional resin layer,furthermore, the thermosetting matrix resin will ooze out to developtackiness between bases.

A composite prepreg base such as those described in detail above,specifically a composite prepreg base that comprises a prepreg baseproduced from a fiber sheet composed of discontinuous reinforcing fibershaving a fiber length in the range of 1 to 300 mm aligned in onedirection and the matrix resin impregnated into the fiber sheet,combined with an additional resin layer formed over at least one of thesurfaces of the prepreg base, can be produced by the production process1, production process 2 or production process 3 described below.

Production Process 1:

A composite prepreg base production process comprising the steps of

-   -   (1-a) preparing a prepreg base comprising a fiber sheet of        continuous reinforcing fibers arranged in one direction and a        matrix resin impregnated at least partly into the fiber sheet,    -   (1-b) forming an additional resin layer on at least one of the        surfaces of the prepreg base prepared in the step (1-a), and    -   (1-c) forming cuts into the prepreg base having the additional        resin layer formed in the step (1-b) to form discontinuous        reinforcing fibers having a fiber length of 1 to 300 mm from the        continuous reinforcing fibers.

Production Process 2:

A composite prepreg base production process comprising the steps of:

-   -   (2-a) preparing a prepreg base comprising a fiber sheet of        continuous reinforcing fibers arranged in one direction and a        matrix resin impregnated at least partly into the fiber sheet,    -   (2-b) forming cuts into the prepreg base prepared in the step        (2-a) to form discontinuous reinforcing fibers having a fiber        length of 1 to 300 mm from the continuous reinforcing fibers,        and    -   (2-c) forming an additional resin layer on at least one of the        surfaces of the prepreg base having the discontinuous        reinforcing fibers having the fiber length of 1 to 300 mm        prepared in the step (2-b).

Production Process 3:

A composite prepreg base production process comprising the steps of:

-   -   (3-a) preparing a fiber sheet of discontinuous reinforcing        fibers having a fiber length of 1 to 300 mm and arranged in one        direction, wherein the edges of the fibers having the fiber        length are located at different positions in the length        direction,    -   (3-b) forming a prepreg base by impregnating a matrix resin at        least partially into the fiber sheet prepared in the step (3-a),        and    -   (3-c) forming an additional resin layer on at least one of the        surfaces of the prepreg base formed in the step (3-b).

In all production processes, the additional resin layer is preparedseparately from the raw prepreg base, and this makes it possible toproduce an additional resin layer having a stable thickness and to layit precisely on the surface of the raw prepreg. The stable thickness ofthe additional resin layer serves to achieve a required flowability andstrength stably during a molding process, making it possible to producea composite prepreg base having high quality stability.

Even if the same resin is used for the matrix resin of the raw prepregbase and the additional resin layer, it will be possible in some casesto concentrate the resin on a surface of the prepreg base by supplyingexcessive quantities of the matrix resin when preparing the raw prepregbase. If the matrix resin is a thermosetting resin, however, this willresult only in an overall increase of the resin content in the rawprepreg base, failing in stable concentration of the resin on thesurface. The effect will not be achieved if the resin is notconcentrated on the surface.

If the matrix resin is a thermoplastic resin, it will be so high inviscosity that it will not be impregnated smoothly into the reinforcingfibers, and therefore, it will be easily concentrated on the surface.But in such cases, it will be very likely that the concentration of theresin on a surface results in some unimpregnated portions being left inthe prepreg base. If unimpregnated portions are left in the prepreg basebefore a molding process and in addition, a thermoplastic resin having ahigh viscosity is used as the matrix resin, it will be difficult toeliminate these unimpregnated portions during an FRP molding process. Ifthe matrix resin is supplied in excessive quantities for concentrationof the resin on a surface of the prepreg base, on the other hand, theprocess stability will be low, and only the thickness of the resin layeron the surface will tend to fluctuate to cause meandering of fibers,which is not desirable.

Suitable methods to put cuts in the production steps (1-c) or (2-b)include the use of a cutter by hand, the use of a cutting machine or apunching machine for mechanical operations, and the use of rotatingroller blades etc. provided at predetermined positions to performcontinuous cutting during the preparation of a raw prepreg base composedof continuous fibers. The use of a cutter by hand is suitable if simpleoperation is desired for putting cuts in the prepreg base while the useof a cutting machine, punching machine, rotating roller blades etc. issuitable for large-scale production with high production efficiency.

The layered base comprises a laminate of two or more plates of thecomposite prepreg base wherein the plates of the composite prepreg baseare integrated by at least partial adhesion and an additional resinlayer is formed on at least one of the surfaces of the layered basesurface.

In a layered base, it is preferable that the matrix resin of the rawprepreg base is thermo-setting resin while the additional resin layercomprises thermoplastic resin, with the thermo-plastic resin exposed ata surface of the layered base. The use of the thermosetting resin as thematrix resin ensures adhesiveness with the reinforcing fibers, as wellas the dimensional stability, heat resistance and creep resistance,while high-ductility thermoplastic resin exists at the ends of thediscontinuous reinforcing fibers on the surface that are likely to actas the starting points of destruction, serving very effectively toproduce FRP products having highly improved strength.

The use of a thermoplastic resin in a form of fiber (such as a nonwovenfabric in particular,) or particles as an additional resin layer allowsthe thermosetting matrix resin to ooze out to develop tackiness on thesurface of the layered base. Production of a layered base will also beeasy when an additional resin layer comprising a thermoplastic resin ina form of fiber (in particular, a nonwoven fabric being preferable) orparticles is provided particularly between layers in the layered base,because the composite prepreg base will have tackiness. Furthermore,when an FRP product is joined to another FRP product, the additionalresin layer of the FRP product is adhered strongly to the other FRPproduct into an integrated body particularly in the case where the otherFRP product comprises a thermoplastic matrix resin. This example can besaid to be an unexpected advantage.

Another example is a layered base comprising reinforcing fibers and amatrix resin wherein two or more raw prepreg bases composed ofdiscontinuous reinforcing fibers oriented in one direction with anadditional resin layer provided at least at one of the interfacesbetween the laminated layers, and two adjacent raw prepreg bases and/oran raw prepreg base and an adjacent additional resin layer are adheredat least partly to integrate them into a layered base, with anadditional resin layer being provided on at least one of the surfaces.

As described previously, integrating composite prepreg bases will have ahandleability during an FRP molding process and can be molded into anintended FRP product while maintaining a designed laminate structure. Ifthe matrix resin is thermosetting resin in this case, its tackinessserves to easily integrate two or more composite prepreg bases.

There are no specific limitations on the laminate structure of thecomposite prepreg bases in the layered base if the laminate is properlystructured to meet the requirements for an intended FRP product. Inparticular, uniform mechanical properties can be achieved and warp inthe FRP is prevented if the laminate has a quasi-isotropic structuresuch as [−45/0/+45/90]_(S) and [+60/0/−60]_(S).

The additional resin layer in the layered base may be provided on onlyone surface or both surfaces of the layered base. It should preferablybe provided on both surfaces in consideration of the friction resistancebetween the composite prepreg base and the mold during an FRP moldingprocess. The additional resin layer is not necessarily at all interfacesbetween adjacent the raw prepreg bases in the layered base, but shouldbe provided only at the interfaces where it is required. To maximize theeffect, it is preferable an additional resin layer is provided at allinterfaces. A layered base in which an additional resin layer isprovided on both surfaces and at all interfaces can be said toconstitute the most preferable example because it can have excellentmolding characteristics.

It is preferable that an additional resin layer is provided at two ormore interfaces between adjacent raw prepreg bases that these additionalresin layers have different thicknesses. It is more preferable thatthick and thin additional resin layers coexist at the interfaces in thelayered base. Better molding characteristics can be achieved and voidscan be prevented from being formed around the ends of discontinuousreinforcing fibers if a thicker additional resin layer is provided atinterfaces where the raw prepreg bases must slip most largely and in theportions where the entire raw prepreg base must be extended most largelyin the orientation direction of the reinforcing fibers. This can be saidto be one of the most preferable examples.

If an additional resin layer is provided both at the interface betweentwo adjacent raw prepreg bases and at least one of the surfaces of thelayered base, it is preferable the additional resin layer provided atthe surface of the layered base is thicker than that at the interface.This is because at the interface between two adjacent raw prepreg bases,the raw prepreg base exists on both sides of the interface to supplyresin easily while at the outermost face of the layered base, the rawprepreg base exists on only the upper or lower side, leading to lessamounts of resin supply. This is preferable to produce FRP productshaving high surface quality, and can be said to constitute one of themost preferable examples.

An FRP is produced by heating and pressing the layered base andcomprises a layered base and an additional resin layer formed on atleast one of its surfaces. The effect is maximized by molding thecomposite prepreg base and a layered base by heating and pressing. Theflowability of the surface layer of the layered base can be increasedand a high-quality FRP can be obtained by providing an additional resinlayer on the surface. As described later, this also makes it possible toproduce an FRP having high adhesiveness to other FRP products.

The FRP is used preferably to produce a shaped product comprising theFRP carrying at its surface an additional resin layer adhered to anotherFRP material or another thermoplastic resin molding to form anintegrated structure. The FRP has an additional resin layer on itssurface, and therefore, it can be combined strongly and easily withanother FRP material or another thermoplastic resin with the additionalresin layer acting in between. Adhering another FRP material to thesurface of the FRP serves to develop functions that cannot be achievedby the FRP alone, such as for producing products of a complicated shape,Class A surfaces for automobiles, and other surfaces of extremely highsurface quality.

Specifically, preferable examples include products where the additionalresin layer in the FRP and the matrix resin in the another FRP materialare thermoplastic resin. If both are thermoplastic resin, extremely highadhesive strength attributed to their thermoplasticity can be achievedto serve for strong and easy adhesion between the FRP and the anotherFRP material.

In a more preferable example, the matrix resin of the FRP is athermosetting resin while the additional resin layer comprises athermoplastic resin, with the thermoplastic resin being exposed at asurface of the layered base, and in addition, the matrix resin of theother FRP is a thermoplastic resin. If a very complicated shape isintended, it is preferable that the other FRP is an injection-moldingproduct composed of discontinuous reinforcing fibers that are randomlydispersed.

In the FRP, it is preferable that the gaps between ends of adjacentdiscontinuous reinforcing fibers are filled with the resin thatconstitutes the additional resin layer. In such an example, it will bepossible to decrease the void fraction and undulation of the layerswhile increasing the elastic modulus as well as the strength. At thesurface of the FRP, furthermore, the formation of shallow depressionsaround the ends of discontinuous reinforcing fibers can be prevented toprovide an FRP having improved surface quality.

For the FRP, it is preferable that the layered base is shaped andsolidified, and as described later, molded into a shape having ribs orquadric surfaces. The use of the composite prepreg base and the layeredbase is of particular significance when producing FRP moldings of acomplicated shape having ribs or quadric surfaces, and this is one ofthe very problems to be solved.

Suitable FRP production methods for the composite prepreg base or thelayered base include press molding, autoclave molding and sheet windingmolding. In particular, press molding preferable because high productionefficiency can be achieved. Specifically, the thickness of the layeredbase is decreased by press molding, leading to thinner layers. As layersbecome thinner, the thickness of the ends of discontinuous reinforcingfibers will decrease, which further prevents crack formation andinterlaminar separation, resulting in an FRP having improved strength.It also serves to minimize the formation of voids.

To carry out such press molding to produce void-free FRP products havinggood appearance quality that have a complicated shape having ribs orquadric surfaces, it is preferable to press the layered base in a moldof a shape having ribs and/or quadric surfaces. The layered base isdesigned to achieve the first to fourth effects, and therefore,void-free FRP products of a complicated shape having ribs or quadricsurfaces can be produced by simply pressing it in the mold. Thisrepresents one of the characteristic features.

Suitable uses of the composite prepreg base and the layered base, andthe FRP produced from them, include structural elements that have acomplicated shape containing ribs and quadric surfaces, such as those oftransport equipment (automobile, aircraft, naval vessels etc.),industrial machines, precision equipment and sports equipment (bicycleetc.). Particularly suitable uses include the crank and frame ofbicycles, head of golf clubs, door and sheet frame as structuralelements of automobiles, and robot arm as structural elements ofindustrial machines.

The disclosure is described more specifically below by referring toexamples, though they are not intended to place any limitations on thedisclosure.

In the examples, when a composite prepreg base a is produced by applyingan additional resin layer to a prepreg base comprising a fiber sheet ofcontinuous reinforcing fibers oriented in one direction and a matrixresin impregnated in the fiber sheet, followed by putting cuts in thecontinuous reinforcing fibers, the prepreg base comprising continuousreinforcing fibers and carrying an additional resin layer is referred toas a preliminary prepreg base.

On the other hand, when a composite prepreg base a is produced bypreparing a prepreg base comprising a fiber sheet of discontinuousreinforcing fibers having a fiber length of 1 to 300 mm oriented in onedirection and a matrix resin impregnated into the fiber sheet, followedby applying an additional resin layer, the prepreg base comprisingdiscontinuous reinforcing fibers is referred to as a raw prepreg base.

Evaluation Method for Flowability

Pieces having a diameter of 100 mm are cut out of the composite prepregbase. A layered product is prepared by laminating eight pieces of thecomposite prepreg base in a quasi-isotropic manner. The layered producthas a laminate structure of [−45/0/+45/90]_(1S). The layered product isthen placed on a flat plate mold of 300×300 mm, and cured the resin at150° C. for 30 minutes under a pressure of 6 MPa in a heater-type pressmolding machine. The ratio of a diameter L (in mm) of the resulting FRPto the original diameter of 100 mm is calculated. The formula forcalculating of the ratio is described as L/100 mm. For the diameter L(in mm) of the resulting FRP, measurements are taken from the outmostcomposite prepreg base layers, and the larger one is used as thediameter L. If the outmost a composite prepreg base layers flow anddeform into an ellipse, then the largest of the major axis measurementsis used as the diameter L. The ratio calculated is then used to evaluatethe flowability.

Evaluation Method for Rib Moldability

From the composite prepreg base, 80 mm×80 mm pieces either in the samedirection as the orientation direction of the reinforcing fibers (0°direction) or in the direction inclined by 45° from the orientationdirection of the reinforcing fibers (45° direction) are cut out. Alayered product is prepared by laminating eight pieces of the compositeprepreg base in a quasi-isotropic manner. The layered product has alaminate structure of [−45/0/+45/90]_(1S). A mold composed of a 100×100mm upper mold having a cavity of 1.5 mm wide, 100 mm long and 15 mm deepprovided in the bottom face and a lower mold having a flat top face isprepared. The layered product is placed on the top face of the lowermold, and the upper mold is put in place, followed by curing the resinin a heater-type press molding machine at 150° C. for 30 minutes under apressure of 6 MPa. The height of the rib formed in the resulting FRP ismeasured. The height measurements are then used to evaluate the ribmoldability.

Evaluation Method for Mechanical Characteristics

Test pieces for tensile strength having a length of 250±1 mm and widthof 25±0.2 mm are cut out of a flat plate FRP. The tensile strength ismeasured according the test method specified in JIS K7073-1988 “Tensiletest method carbon fiber reinforced plastics” under the conditions of agage length of 150 mm and a crosshead travel rate of 2.0 mm/min. A Model4208 Instron (registered trademark) type universal tester is used forthe testing in the Examples. The number n of test pieces subjected tomeasurement is 10, and the average for them is used as the value oftensile strength. Furthermore, the standard deviation is calculated fromthe measurements, and the standard deviation is then divided by theaverage to determine the variation coefficient CV (%), which indicatesthe degree of variation.

Evaluation Method for Minimum Viscosity of a Resin

The minimum viscosity is determined from the relational curve fortemperature and viscosity under the conditions of a heating rate of 2°C./min, vibration frequency of 0.5 Hz and use of parallel plates (40 mmdiameter). An expansion-type ARES viscoelasticity measuring systemsupplied by Rheometric Scientific Inc. is used for measurement in theExamples.

Evaluation Method for Thickness of an Additional Resin Layer

The cross section is observed directly with an optical microscope (400magnifications) to determine the thickness.

Evaluation Method for G_(IC) of a Matrix Resin

Plates (2±0.1 mm thickness, 10±0.5 mm width, 120±10 mm length) are cutout of a cured resin and used as test pieces. The tensile modulus E andPoisson's ratio v of the test pieces are measured according to themethod specified in JIS K7161-1994 “Plastics—Test method for tensilecharacteristics.” Similarly, the K_(IC) is measured for the plates ofheat-cured resin (6±0.3 mm thickness, 12.7±0.3 mm width and 80±10 mmlength) according to ASTM D5045-99. The value of G_(IC) is calculatedfrom the measurements of the tensile modulus E, Poisson's ratio υ andK_(IC) by the formula ((1−υ)²×K_(IC) ²)/E. The times n of measurementsis 10.

Evaluation Method for G_(IIC) of an FRP

To take measurements, the ENF test (flexure test for end-notched testpieces) is carried out according to the method specified in Appendix 2to JIS K7086-1993 “Interlaminar fracture toughness test method forcarbon fiber reinforced plastics.” The times n of measurements is 10.

EXAMPLE 1

In a kneader, an epoxy resin (30 parts by weight of “Epikote (registeredtrademark)” 828, 35 parts by weight of “Epikote (registered trademark)”1001, and 35 parts by weight of “Epikote (registered trademark)” 154,manufactured by Japan. Epoxy Resins Co., Ltd.), 5 parts by weight of athermoplastic resin of polyvinyl formal (Vinylec K (registeredtrademark) manufactured by Chisso Corporation), 3.5 parts by weight of adicyandiamide curing agent (DICY7 manufactured by Japan Epoxy ResinsCo., Ltd.), and 4 parts by weight of a curing accelerator3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU99 manufactured byHodogaya Chemical Co., Ltd.) were heat-kneaded to prepare an epoxy resincomposition 1, which was uncured material containing polyvinyl formaldissolved uniformly. The epoxy resin composition 1 was spread over arelease paper with a reverse roll coater to prepare a resin film 1 of 19g/m².

Then, the resin film 1 was laid on both sides of carbon fibers (tensilestrength of 4,900 MPa, tensile modulus of 235 GPa) 3 oriented in onedirection, followed by heating and pressing (130° C., 0.4 MPa) forimpregnation of the resin to prepare a prepreg base 1 having a carbonfiber unit weight of 120 g/m², a matrix resin content of 24 wt %, and aprepreg base thickness of 0.12 mm.

The same material as the uncured epoxy resin composition 1 was spreadover a release paper with a reverse roll coater to prepare a resin film(a resin unit weight of 19 g/m², and a film thickness of 0.02 mm),which, used as an additional resin layer 10, was applied to one side ofthe prepreg base 1 to prepare a preliminary prepreg base 1 (a resincontent of 32 wt %, a prepreg base thickness of 0.14 mm).

Subsequently, cuts were put continuously in the resulting preliminaryprepreg base 1 as shown in FIG. 3 using an automatic cutting machine toproduce a composite prepreg base 1 having regularly arranged cuts 40aligned at equal intervals.

The cuts 40 are put in the perpendicular direction 2 to the orientationdirection 1 of the fibers 3, and the length of the cuts 40 and the fiberlength 6 of the fibers 3 after being cut are 10.5 mm and 30 mm,respectively. Adjacent cut-rows 50 are shifted by 10 mm in the direction2 perpendicular to the orientation direction 1 of the fibers 3. Thus,there are two types of, patterns of cuts in many cut-rows 50.Furthermore, the cuts 40 in the adjacent cut-rows 50 extend 0.5 mm eachother. The number of fibers 3 cut by each cut is 18,900.

The epoxy resin composition 1 had a minimum viscosity of 5.5 Pa·s, andthe composite prepreg base 1 had tackiness. A cured product (130° C., 90min) of the epoxy resin composition 1 itself had a Mode I fracturetoughness G_(IC) of 174 J/m².

From the composite prepreg base 1 produced, 250×250 mm pieces either inthe same direction as the orientation direction of the carbon fibers 3(0° direction) or in the direction shifted by 45° from the orientationdirection of the carbon fibers 3 (45° direction) are cut out. Sixteencut out composite prepreg bases 1 are laminated in a quasi-isotropicmanner in such a way that the face of a base that carries the additionalresin layer 10 comes in contact with the face of the adjacent base thatis free of the additional resin layer, providing a layered base 1. Thelaminate structure was [−45/0/+45/90]_(1S). The layered base 1 had athickness of 2.2 mm. The layered base 1 was then placed on a flat platemold of area of 300×300 mm, and cured the resin at 150° C. for 30minutes under a pressure of 6 MPa in a heater-type press molding machineto provide a flat plate FRP having an area of 300×300 mm and a thicknessof 1.6 mm.

The resulting flat plate FRP was free of undulation of carbon fibers,and the carbon fibers had flowed uniformly and sufficiently to the edgeof the FRP. It was free of warp, and had a highly smooth flat surface.The flowability was 1.3, and the height of the ribs formed was 10 mm.The tensile strength of the FRP was 390 MPa, and the variationcoefficient CV was as small as 6%.

In addition, 10 trays that had a width of 80 mm, length of 160 mm, wallheight of 20 mm and quadric surface having a curvature radius (R) of 3mm were produced successively under the same molding conditions asabove. In the resulting trays, all quadric portions and all gaps betweenthe ends of adjacent discontinuous carbon fibers, even in the outermostface, were completely filled with the resin without leaving emptyspaces, and the wall portions were also free of creases, indicating thatthe FRP products produced had high appearance quality. The fact thathigh quality FRP products were obtained in all the 10 molding runsproved their high quality stability.

EXAMPLE 2

In a kneader, an epoxy resin (9 parts by weight of “Epikote (registeredtrademark)” 828, 35 parts by weight of “Epikote (registered trademark)”1001, 20 parts by weight of “Epikote (registered trademark)” 1004, and36 parts by weight of “Epikote (registered trademark)” 807, manufacturedby Japan Epoxy Resins Co., Ltd.), 5 parts by weight of a thermoplasticresin of polyvinyl formal (Vinylec K (registered trademark) manufacturedby Chisso Corporation), 4.5 parts by weight of a dicyandiamide curingagent (DICY7 manufactured by Japan Epoxy Resins Co., Ltd.), and 3 partsby weight of a curing accelerator 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU99 manufactured by Hodogaya Chemical Co., Ltd.) wereheat-kneaded to prepare an epoxy resin composition 2 (resin minimumviscosity 3.4 Pa·s), which was uncured material containing polyvinylformal dissolved uniformly.

Using this epoxy resin composition 2, the same procedure as in Example 1was carried out to produce a prepreg base 2 (tensile strength of carbonfibers 4,900 MPa, tensile modulus 235 GPa, unit weight of carbon fibers150 g/m², matrix resin content 24 wt %, thickness of a prepreg base 0.14mm).

In another kneader, an epoxy resin (35 parts by weight of “Epikote(registered trademark)” 828, 30 parts by weight of “Epikote (registeredtrademark)” 1001, and 35 parts by weight of “Epikote (registeredtrademark)” 154, manufactured by Japan Epoxy Resins Co., Ltd.), 3 partsby weight of a thermoplastic resin of polyvinyl formal (Vinylec K(registered trademark) manufactured by Chisso Corporation), 3.5 parts byweight, of a dicyandiamide curing agent (DICY7 manufactured by JapanEpoxy Resins Co., Ltd.), and 3 parts by weight of a curing accelerator3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU99 manufactured byHodogaya Chemical Co., Ltd.) were heat-kneaded to prepare an epoxy resincomposition 3 having a minimum viscosity of 1.5 Pa·s, which was uncuredmaterial containing polyvinyl formal dissolved uniformly.

Over both surfaces of the prepreg base 2, an additional resin layer thatwas in the form of resin film (unit weight 19 g/m², film thickness 0.02mm) produced by spreading the uncured epoxy resin composition 3 having alower viscosity than the matrix resin over a release paper with areverse roll coater was laid to produce a preliminary prepreg base 2 (aresin content of 31 wt %, a prepreg base thickness of 0.18 mm).

Except that the preliminary prepreg base 2 was used, the same procedureas in Example 1 was carried out to produce a composite prepreg base 2,which was then used to produce a layered base 2, and a flat plate FRPwas produced by molding the layered base 2. The composite prepreg base 2of this Example carried an additional resin layer on both surfaces, andlamination operation was performed efficiently because no differencesexisted between the two sides.

The resulting flat plate FRP was, as the case of Example 1, free ofundulations of carbon fibers and had flowed uniformly and sufficientlyto the edge of the FRP. It was also free of warp, and had a highlysmooth flat surface. For molding characteristics, the flowability was1.5, and the height of the ribs formed was 15 mm, and it was confirmedthat the cavity was filled with the composite prepreg base 2 up to theupper limit during the molding process. The tensile strength of the FRPwas 410 MPa, which is higher than that in Example 1 because of a highercarbon fiber content, while the variation coefficient CV was 9%.

EXAMPLE 3

In a kneader, an epoxy resin (90 parts by weight of ELM 434 manufacturedby Sumitomo Chemical Co., Ltd., and 10 parts by weight of Epicron 830manufactured by Dainihon Ink Chemical Co., Ltd), 15 parts by weight of athermoplastic polyether sulfone resin (Sumikaexcel PES5003P manufacturedby Sumitomo Chemical Co., Ltd.), and 35 parts by weight of a 4,4%diaminodiphenyl sulfone curing agent (Sumicure S manufactured bySumitomo Chemical Co., Ltd.) were heat-kneaded to prepare an epoxy resincomposition 4 (resin minimum viscosity 0.4 Pa·s), which was uncuredmaterial containing polyether sulfone dissolved uniformly.

Using this epoxy resin composition 4, the same procedure as in Example 1was carried out to produce a prepreg base 3 (tensile strength of carbonfibers 5,400 MPa, tensile modulus 294 GPa, unit weight of carbon fibers150 g/m², matrix resin content 25 wt %, thickness of a prepreg base 0.14mm).

Cuts were put in this prepreg base while a resin composition produced byheat-kneading the same resin composition as the uncured epoxy resincomposition 4 and spherical particles of polyamide 12 (a median diameter(D50) of 7 μm as determined by laser diffraction/scattering) to act asfiller was spread over a release paper with a reverse roll coater toprepare a resin film (unit weight of resin 40 g/m², film thickness 0.04mm, 13 g/m² of spherical particles of polyamide 12 contained in theresin film), which was then used as additional resin layer and appliedto one of the surfaces of the raw prepreg base that contained cuts,providing a composite prepreg base 3 (resin content 35 wt %, thicknessof a prepreg base 0.18 mm).

Using the composite prepreg base 3, the same procedure as in Example 1except that the resin was cured under the conditions of 185° C. and 120minutes was carried out to provide a composite prepreg base 3 and alayered base 3, followed by molding them into a flat plate FRP. A curedproduct (180° C., 120 min) of the epoxy resin composition 4 itself andthe resin itself that constitutes the additional resin layer had a ModeI fracture toughness G_(IC) of 124 J/m² and 590 J/m², respectively.

The resulting flat plate FRP was, as the case of Example 1, free ofundulations of carbon fibers, and the carbon fibers had flowed uniformlyand sufficiently to the edge of the FRP. It was also free of warp, andhad a highly smooth flat surface. However, the FRP was slightly inferiorin appearance quality that that produced in Example 1. For moldingcharacteristics, the flowability was 1.4, and the height of the ribsformed was 15 mm, and it was confirmed that the cavity was filled withthe composite prepreg base 2 up to the upper limit during the moldingprocess. The tensile strength of the FRP was as high as 490 MPa, and thevariation coefficient CV was 8%. The Mode II the fracture toughnessG_(IIC) of the FRP was 2.4 kJ/m².

In 10 trays produced successively by the same procedures as in Example1, the resulting trays, all quadric portions and all gaps between theends of adjacent discontinuous carbon fibers, even in the outermostface, were completely filled with the resin without leaving emptyspaces, and the wall portions were also free of creases, indicating thatthe FRP products produced had high appearance quality. The fact thathigh quality FRP products were obtained in all the 10 molding runsproved their high quality stability.

EXAMPLE 4

Except that the unit weight of carbon fiber was 80 g/m² and the layeredbase had a structure of [−45/0/+45/90]_(3S), the same procedure as inExample 1 was carried out to produce a flat plate FRP.

The resulting flat plate FRP was, as the case of Example 1, free ofundulations of carbon fibers, and the carbon fibers had flowed uniformlyand sufficiently to the edge of the FRP. It was also free of warp, andhad a highly smooth flat surface. The flowability was 1.4, and theheight of the ribs formed was 15 mm. The tensile strength of the FRP was420 MPa, and the variation coefficient CV was 5%, indicating that thevariation was small.

EXAMPLE 5

A prepreg base was prepared from the uncured epoxy resin composition 1,and cuts were put in the prepreg base without applying resin film to it,followed by laminating sixteen the cut-containing raw prepreg bases in aquasi-isotropic manner to produce a layered product. The layered producthad a structure of [−45/0/+45/90]_(2S). In producing the layeredproduct, the same resin as the uncured epoxy resin composition 1 andspherical glass particles (acting as filler, average diameter 15 μm)subjected to epoxy silane coupling were heat-kneaded to prepare a resincomposition, and it was then spread over a release paper with a reverseroll coater to provide a total of five sheets of resin film (unit weightof resin 25 g/m², film thickness 0.025 mm, containing 10 g/m² of glassspherical particles subjected to epoxy silane coupling), which were usedas the outmost, fourth, eighth and twelfth layers of the resultinglayered base. Except this, the same procedure as in Example 1 wascarried out to produce a layered base, which was molded into a flatplate FRP.

The resulting flat plate FRP was, as the case of Example 1, free ofundulations of carbon fibers, and the carbon fibers had flowed uniformlyand sufficiently to the edge of the FRP. It was also free of warp, andhad a highly smooth flat surface. For the molding characteristics, theflowability was 1.3, and the height of the ribs formed was 10 mm.However, the FRP was slightly poorer in appearance quality than thatproduced in Example 1. The tensile strength of the FRP was 400 MPa, andthe variation coefficient CV was 6%, indicating that the variation wassmall.

EXAMPLE 6

Except that the uncured epoxy resin composition 1 together with sliveryarns (fiber length from 10 mm to 150 mm) produced by a draft zonesystem spinning as reinforcing fibers instead of continuous carbonfibers, that the uncured epoxy resin composition 1 was spray-coated in aparticle-like state (unit weight of resin 10 g/m², film thickness 0.03mm) to act as the additional resin layer instead of resin film, and thatcuts were not put in it, the same procedure as in Example 1 was carriedout to produce a composite prepreg base and a layered base, which werethen molded into a flat plate FRP.

The resulting FRP was, as the case of Example 1, free of undulations ofcarbon fibers, and the carbon fibers had flowed uniformly andsufficiently to the edge of the FRP. It was also free of warp, and had ahighly smooth flat surface. For the molding characteristics, theflowability was 13, and the height of the ribs formed was 6 mm. Thetensile strength of the FRP was as high as 630 MPa, and the variationcoefficient CV was 5%.

EXAMPLE 7

Before applying the additional resin layer to the raw prepreg base 1produced in Example 1, the same procedure as in Example 1 was carriedout to put cuts continuously using an automatic cutting machine as shownin FIG. 3 to produce a raw prepreg base 1 containing regularly-arrangedcuts at equal intervals. Then, copolymerized polyamide resin (“Amilan”(registered trademark) CM4000, polyamide copolymer having a meltingpoint of 155° C. manufactured by Toray Industries, Inc.) was meltblowninto a nonwoven fabric having a weight per unit area of 20 g/m². Thisnonwoven fabric was applied to one surface of the cut-containing rawprepreg base 1, and they were pressed with a nip roller at roomtemperature to integrate them into a composite prepreg base.

The resulting composite prepreg bases were laminated to prepare alayered base as in Example 1. A surface of the prepreg base comprisingthe thermosetting matrix resin was adhered to that of the nonwovenfabric used as the additional resin layer to form an interface. Becausethe additional resin layer was the nonwoven fabric, the compositeprepreg base had tackiness as a result of oozing of the matrix resin,leading to good lamination operation conditions as in Example 1. Thesame procedure as in Example 1 was carried out to mold an FRP product.Because the thermoplastic resin was used in the additional resin layer,the mold was cooled to about 100° C. before removing the product.

The resulting FRP was, as the case of Example 1, free of undulations ofcarbon fibers, and the carbon fibers had flowed uniformly andsufficiently to the edge of the FRP. It was also free of warp, and had ahighly smooth flat surface. The flowability was 1.3, and the cavity forthe rib was filled up to a height of 12 mm. The tensile strength of theFRP was as high as 460 MPa, and the variation coefficient CV was 5%.

EXAMPLE 8

The flat plate FRP produced in Example 7 was placed in an injectionmold, and polyamide 6 pellets kneaded with carbon fibers (pellets of“Torayca” (registered trademark) manufactured by Toray Industries, Inc.,carbon fiber weight content of 20 wt %, randomly dispersed discontinuouscarbon fibers, fiber length of 0.2 mm), used as another FRP, wereinjected onto the surface of the additional resin layer adhered on theflat plate FRP to produce a complicated T-shape rib of the another FRPformed on the flat plate FRP. The polyamide 6 containing carbon fibers,i.e., the another FRP, is adhered to the additional resin layer on theflat, plate FRP to form an integrated product, and the vertical adhesionstrength (flatwise peel strength) between them was as high as 10 MPa ormore, indicating an extremely high adhesiveness.

EXAMPLE 9

A sheet of polycarbonate (“Lexan” (registered trademark) SLXmanufactured by GE Plastics Co., Ltd.), used as the anotherthermoplastic resin, was placed on the surface of the additional resinlayer on the layered base produced in Example 7 and cured at 110° C. for90 minutes under a pressure of 1 MPa to produce a flat plate FRP havingextremely high surface quality that had a sheet adhered over itssurface. During the molding of the layered base into a flat plate FRP,the additional resin layer entered into the reinforcing fibers andadhered to the polycarbonate sheet, which was a molding of the anotherthermoplastic resin, to form an integrated product. Their adhesionstrength (shear peel strength) according to 1SO4587 was as high as 5 MPaor more, indicating high adhesiveness.

Comparative Example 1

Except that resin film was used as the additional resin layer on thepreliminary prepreg base 3, the same procedure as in Example 3 wascarried out to produce a flat plate FRP.

The resulting flat plate FRP was free of undulations of carbon fibers,and the carbon fibers had flowed uniformly and sufficiently to the edgeof the FRP. The flowability was 1.2, and the height of the rib was 5 mm,which were inferior as compared with Examples 1 and 3. The tensilestrength of the FRP was 390 MPa, and the variation coefficient CV was6%. It had nearly the same level of mechanical characteristics as thosein Example 1. The Mode II fracture toughness G_(IIC) was 0.9 kJ/m².

Trays produced by the same procedure as in Example 1 were free ofcreases in the quadric portion next to the wall portion, but in theoutermost surface, some of the gaps between the ends of adjacent bundlesof discontinuous carbon fibers contained spaces free of matrix resin inall of 10 trays, resulting in slightly poorer appearance quality than inExamples 1 and 3.

Comparative Example 2

The same epoxy resin and the same step as in Example 1 were used toproduce a prepreg base 4 having a unit weight of carbon fiber of 120g/m² and matrix resin content of 32 wt %. The matrix resin wasimpregnated uniformly in the reinforcing fibers, and the surface wasfree of localized resin portions.

Without providing the additional resin layer, the same procedures as inExample 1 was carried out to put cuts continuously in the prepreg base 4with an automatic cutting machine as shown in FIG. 3, and thus theresulting prepreg base 4 had regularly-arranged cuts at equal intervals.Except that the additional resin layer was formed, the same procedure asin Example 1 was carried out to produce a flat plate FRP.

The resulting flat plate FRP was free of undulations of carbon fibers,and the carbon fibers had flowed uniformly and sufficiently to the edgeof the FRP. The flowability was 1.2, and the height of the rib was 8 mm,which were inferior as compared with Examples 1 and 3. The tensilestrength of the FRP was 370 MPa, and the variation coefficient CV was5%. It had nearly the same or lower level of mechanical characteristicsas compared with those in Example 1.

Trays produced by the same procedure as in Example 1 were free ofcreases in the quadric portion next to the wall portion, but in theoutermost surface, some of the gaps between the ends of adjacentdiscontinuous carbon fibers contained spaces free of matrix resin infive of 10 trays, resulting in slightly poorer appearance quality thanin Examples 1 and 3.

Comparative Example 3

The nonwoven fabric produced from the thermoplastic resin used inExample 7 was used as a matrix resin. The same carbon fibers as inExample 1 were stretched parallel to each other in one direction to forma sheet having a unit weight of carbon fiber of 120 g/m², and twononwoven fabric sheets of 20 g/m² were applied to each surface (totaling4 sheets), followed by heating the matrix resin with a nip rolleradjusted at 160° C. to lower the viscosity and achieve impregnation.Thus, a prepreg base 5 having a matrix resin content of 40 wt % wasproduced. Though the matrix resin was localized on the surface of theprepreg base 5, the thickness was not uniform and undulations of fiberswere found. The prepreg base 5 was severed to observe the cross section,and it was found that some central portions in the thickness directionwere left unimpregnated with the resin.

Without providing the additional resin layer, the same procedures as in.Example 1 was carried out to put cuts continuously in the prepreg base 5with an automatic cutting machine as shown in FIG. 3, and thus theresulting prepreg base 5 had regularly-arranged cuts at equal intervals.Because it was free of tackiness, its bases were simply put one on topof another to form a similar structure to that in Example 1, andpreheated at 180° C. with an infrared heater (IR heater), followed bycold-pressing with a press adjusted to 70° C. to produce a flat plateFRP.

Though the resulting flat plate FRP had undulations of carbon fibers,the carbon fibers had flowed uniformly and sufficiently to the edge ofthe FRP. The tensile strength was 250 MPa, and the variation coefficientCV was 8%, indicating that the mechanical characteristics were very pooras compared with the FRP in Examples 1 and 3. This can be attributed tothe existence of portions unimpregnated with the resin.

Trays similar to those in Example 1 were produced under the sameconditions as for the flat plate FRP. They were free of creases in thequadric portion next to the wall portion, but in the outermost surface,some of the gaps between the ends of adjacent discontinuous carbonfibers contained spaces free of matrix resin in eight of 10 trays,resulting in slightly poorer appearance quality than the FRPs inExamples 1 and 3.

Comparative Example 4

Except that the layered base produced in Comparative Example 1 was used,the same procedure as in Example 9 was carried out to provide a flatplate FRP. The resulting FRP was found integrated with the polycarbonatesheet, i.e., the another thermoplastic resin molding, but the adhesionstrength (shear peel strength) was so low that they could be separatedby hand, indicating poor adhesiveness.

INDUSTRIAL APPLICABILITY

We provide a layered base comprising a plurality of raw prepreg bases,each comprising a fiber sheet comprising discontinuous reinforcingfibers having a fiber length of 1 to 300 mm oriented in one directionand a matrix resin impregnated in the fiber sheet, laminated with anadditional resin layer provided at least on one of the outermostsurfaces and at least in one of the interlayer spaces, wherein at eachinterface, either the two adjacent prepreg bases, or the prepreg baseand the additional resin layer, are adhered at least partly to integratethe entire body, and also provides FRP moldings produced from thelayered base.

We further provide a production process for a composite prepreg basecomprising the raw prepreg base that constitutes the layered base andthe additional resin layer formed on at least one of its surfaces.

In the layered base, the additional resin layer is provided between theraw prepreg bases and at on at least one of the surfaces of the layeredbase, and the raw prepreg base comprises discontinuous reinforcingfibers to allow the discontinuous fibers, the resin that constitutes theadditional resin layer and the matrix resin in the raw prepreg base toflow smoothly to form the shape of the intended moldings accuratelyduring the process for producing the FRP moldings from this a layeredbase. As a result, this facilitates the production of intended moldings,particularly those of a complicated shape.

The resulting moldings can be used effectively as material forstructural elements that have a complicated shape containing ribs andquadric surfaces, such as those of transport equipment (automobile,aircraft, naval vessels etc.), industrial machines, precision equipmentand sports equipment (bicycle, golf outfit, etc.).

1. A method for producing a composite prepreg base comprising a rawprepreg base composed of a fiber sheet of discontinuous reinforcingfibers having a fiber length of 1 to 300 mm and arranged in onedirection and a matrix resin impregnated into the fiber sheet, and anadditional resin layer formed on at least one of the surfaces of the rawprepreg base, which comprises the steps of: (1-a) preparing a prepregbase comprising a fiber sheet of continuous reinforcing fibers arrangedin one direction and a matrix resin impregnated at least partly into thefiber sheet, (1-b) forming an additional resin layer on at least one ofthe surfaces of the prepreg base prepared in the step (1-a), and (1-c)forming cuts into the prepreg base having the additional resin layerformed in the step (1-b) to form discontinuous reinforcing fibers havinga fiber length of 1 to 300 mm from the continuous reinforcing fibers. 2.A method for producing a composite prepreg base comprising a raw prepregbase composed of a fiber sheet of discontinuous reinforcing fibershaving a fiber length of 1 to 300 mm and arranged in one direction and amatrix resin impregnated into the fiber sheet, and an additional resinlayer formed on at least one of the surfaces of the raw prepreg base,which comprises the steps of: (2-a) preparing a prepreg base comprisinga fiber sheet of continuous reinforcing fibers arranged in one directionand a matrix resin impregnated at least partly into the fiber sheet,(2-b) forming cuts into the prepreg base prepared in the step (2-a) toform discontinuous reinforcing fibers having a fiber length of 1 to 300mm from the continuous reinforcing fibers, and (2-c) forming anadditional resin layer on at least one of the surfaces of the prepregbase having the discontinuous fibers having the fiber length of 1 to 300mm prepared in the step (2-b).
 3. A method for producing a compositeprepreg base comprising a raw prepreg base composed of a fiber sheet ofdiscontinuous reinforcing fibers having a fiber length of 1 to 300 mmand arranged in one direction and a matrix resin impregnated into thefiber sheet, and an additional resin layer formed on at least one of thesurfaces of the raw prepreg base, which comprises the steps of: (3-a)preparing a fiber sheet of discontinuous reinforcing fibers having afiber length of 1 to 300 mm and arranged in one direction, wherein theedges of the fibers having the fiber length are located at differentpositions in the length direction, (3-b) forming a prepreg base byimpregnating a matrix resin at least partially into the fiber sheetprepared in the step (3-a), and (3-c) forming an additional resin layeron at least one of the surfaces of the prepreg base formed in the step(3-b).
 4. The method for producing a composite prepreg base according toclaim 1 or 2, wherein the cuts formed in the prepreg base comprises cutshaving a length of 2 to 50 mm arranged with an interval each other incut-rows each of which is directed to a direction across the directionof the arrangement of the reinforcing fibers and which are arranged withan interval each other in the direction of the arrangement of thereinforcing fibers, wherein a distance between two cut-rows that are insuch a relation that when one of them is moved in the direction of thearrangement of the reinforcing fibers, each cut on it meets firstlyanother on the other cut-row, is in the range of 10 to 100 mm; positionsof the cuts in the adjacent cut-rows in the direction of the arrangementof the reinforcing fibers are shifted each other in the directionperpendicular to the direction of the arrangement of the reinforcingfibers; and when the cuts are projected in the direction of thearrangement of the reinforcing fibers, positions of the ends of cuts inthe adjacent cut-rows in the direction of the arrangement of thereinforcing fibers are overlapped each other with an overlap in therange from 0.1 mm to 10% of the length of the shortest of the adjacentcuts in the direction perpendicular to the direction of the arrangementof the reinforcing fibers.
 5. The method for producing a compositeprepreg base according to any one of claims 1 to 3, wherein theadditional resin layer formed on at least one of the surfaces of theprepreg base covers the whole or a part of a surface of the prepreg baseand a thickness of the additional resin layer formed is in the rangefrom the diameter of a single fiber in the reinforcing fibersconstituting the reinforcing fiber sheet to the 0.5 times of a thicknessof the raw prepreg base.
 6. The method for producing a composite prepregaccording to any one of claims 1 to 3, wherein the additional resinlayer contains particulate or fibrous fillers.
 7. The method forproducing a composite prepreg according to any one of claims 1 to 3,wherein a resin constituting the additional resin layer differs from thematrix resin constituting the raw prepreg base, and the minimumviscosity of the resin constituting the additional resin layer, in therange from room temperature to the decomposition temperature, is lowerthan that of the matrix resin.
 8. The method for producing a compositeprepreg according to any one of claims 1 to 3, wherein a resinconstituting the additional resin layer differs from the matrix resinconstituting the raw prepreg base, and a fracture toughness of the resinconstituting the additional resin layer is higher than that of thematrix resin.
 9. The method for producing a composite prepreg accordingto any one of claims 1 to 3, wherein the matrix resin constituting theraw prepreg base is a thermosetting resin, and a resin constituting theadditional resin layer is a thermoplastic resin.
 10. A layered basecomprises a plurality of composite prepreg bases each of which isproduced by a method for producing a composite prepreg base according toany one of claims 1 to 3, in which the composite prepreg bases arelaminated so that the additional resin layer exists on at least one ofthe surfaces of the composite prepreg base, and the adjacent compositeprepreg bases are adhered at least partially to each other.
 11. Thelayered base according to claim 10, wherein thicknesses of theadditional resin layers on at least two composite prepreg bases in theplurality of composite prepreg bases laminated each other are differenteach other.
 12. A layered base comprises a plurality of laminated layerseach of which is composed of a raw prepreg base comprising a fiber sheetof discontinuous reinforcing fibers having a fiber length of 1 to 300 mmand arranged in one direction and a. matrix resin impregnated into thefiber sheet, wherein an additional resin layer is provided on at leastone of the outermost layers and in at least one of interlayer spaces ofthe laminated layers, and at the interlayer spaces of the laminatedlayers, the raw prepreg bases each other and/or the raw prepreg base andthe additional resin layer are adhered at least partially at theinterface between them to be integrated each other.
 13. The layered baseaccording to claim 12, wherein thicknesses of at least two of theadditional resin layers are different each other.
 14. The layered baseaccording to claim 11, wherein a thickness of the additional resin layeron a surface of the layered base is larger than that of the additionalresin layer inside the layered base.
 15. The layered base according toclaim 13, wherein a thickness of the additional resin layer on a surfaceof the layered base is larger than that of the additional resin layerinside the layered base.
 16. The layered base according to claim 10,wherein the matrix resin that constitutes the raw prepreg base is athermosetting resin, and a resin that constitutes the additional resinlayer is a thermoplastic resin which exposes on a surface of the layeredbase.
 17. The layered base according to claim 12, wherein the matrixresin that constitutes the raw prepreg base is a thermosetting resin,and a resin that constitutes the additional resin layer is athermoplastic resin which exposes on a surface of the layered base. 18.A fiber reinforced plastic produced by heating and pressing the layeredbase described in claim 10, wherein an additional resin layer exists onat least one of the surfaces of the layered base.
 19. A fiber reinforcedplastic produced by heating and pressing the layered base described inclaim 12, wherein an additional resin layer exists on at least one ofthe surfaces of the layered base.
 20. The fiber reinforced plasticaccording to claim 18, wherein a resin that constitutes the additionalresin layer exists between the ends of adjacent of the discontinuousfibers of the reinforcing fibers.
 21. The fiber reinforced plasticaccording to claim 19, wherein a resin that constitutes the additionalresin layer exists between the ends of adjacent of the discontinuousfibers of the reinforcing fibers.